My left rear door spontaneously decided to no longer stay closed. It was opened, then refused to close. Good thing I had some tape on me to hold it closed and get home. But now I need to know how to remove the mechanism to service or replace it.

As usual the service manual is utterly useless (seriously why are car manuals so horrible? bike service manuals actually give you useful information and guide you step by step with proper instructions....) so i'm not sure what to be doing exactly. It looks like I can't remove the rear mechanism unless I somehow disconnect the outside door handle, and loosen/remove the inside door handle. I've done the inside handle but the outside one I can't figure out how to disconnect it from the locking mechanism?
Any help?

Pictures would be great, but a write up with some more information than
1) [item name]
2) [item name]
3) [item name]
would be the next best thing

Ok nevermind I figured it out. For anyone who's interested

Remove the door trim
Between the interior door handle, and the central locking motor, there is a white plastic clip which holds the 2 wire arms. Unclip the wire arms from it
Remove the 2 phillips screws on the interior door handle, pull it outwards slightly and you'll see 2 plastic tabs holding the arms in place. You rotate them clockwise and they'll unsnap from the arms, then the arms simply pull out
Get the rear portion of the clear plastic weather backing out of the way
Get a torch and look inside the recess in the door, if you look closely you'll see a zig-zag piece of wire which connects the outside door handle to the door mechanism (pull the handle in and out and you'll see it move). This too has a white plastic tab, again just rotate it clockwise then the arm will pull out. Make sure when you remove the wire arm, that it sits towards the outside of the door mechanism, otherwise it will catch when you try and remove the mechanism
Then remove the 3 phillips screws at the rear of the door which hold the mechanism in place. And simply slide the whole unit out

I'm not sure what its supposed to look like, but I did see some broken plastic on the mechanism. Look at where the outside door handle attached, then follow that down. If you operate that mechanism by hand you'll see it pushes up on a flattened bit of metal (which is supposed to have plastic covering it, this was broken off for me). That piece appears as if it should be spring loaded. Since if you apply pressure to it then you can manually close the door mechanism and it will stay closed. If it has no pressure on it, then it will not close
I simply used a rubber band, strategically wrapped around in such a way that it can't fall off
I then found that the inside door handle worked fine, however the outside door handle did not. This was because the plastic had broken off, leaving too much of a gap (on the same piece I applied the rubber band)
So I put a zip tie around it where the plastic was broken off, to give it a bit of extra thickness. Now both handles operate correctly and the door closes as it should

If the above is too vague a description (sorry, didn't have my phone with me for a photo), then at least you have the mechanism out and can go to a wreckers and get another one

I was going to post after your first post, along the lines of "open it up and have a look" but you've gone and done that! lol Good on you!
Unusual for bits to break off on these, but as you say, visiting a wreckers to get a good one is probably your best option. Should be lots of them about, not a common bit that needs replacing.

Having a look is difficult when the mechanism is inside the door which you can't see or access very easily. But what shits me is the utterly hopeless manual, flat pack shelving has more detailed instruction. It says nothing about unclipping those tabs or that they are even there. It's not even worth reading, it just makes me frustrating after an hour of buggering about with the door and then reading its meaningless instruction

Let me give you the opposite of that, from a page in one of bike service manuals about removing the swingarm

Remove the Frame Covers and seat. (Refer to page 5-1)
Remove the rear wheel. (Refer to page 5-27)
Loosen the carburetor clamp screw (1)
Disconnect the crankcase breather hose (2)
Remove the air cleaner by removing the mounting bolts (3)
Disconnect the brake hose from the hose guides
Remove the drive chain cover and guide
Remove the rear shock absorber lower mounting bolt (4)
Remove the cushion lever mounting nut (5) and bolt
Remove the rear swingarm pivot nut after removing the caps
Remove the rear swingarm by removing the pivot shaft
Remove the rear shock absorber
Remove the cushion rods with cushion lever
Remove the drive chain buffer
Remove the brake hose guides and mud guard
Remove the cushion rods
Remove the cushion lever dust seals and spacers
Remove the swingarm

With pictures of every step and arrows pointing at the bits. Every bike service manual i've ever read has been like that, it takes you through every step.
On the other end of the spectrum, here would be the mitsubishi version..
1) Remove swingarm
[insert pointless picture]
2) Get on google/forum and ask for further instruction on how to do this

The world is a better place when people like you make the effort to share. Good on ya, Mil.7!

I'm glad I could help. Lack of detailed information - especially from a 'service' manual - shits me. If I encounter a step in any process that isn't obvious, then I expect to have the information to tell me what is correct. The Magna/Verada service manual is by far the worst i've ever seen. It's borderline useless for many things

Lack of detailed information - especially from a 'service' manual - shits me.

Don't expect a workshop manual to have a step-by-step procedure for anything you may need to do to your car. It is not meant to be a "how-to" book. Imagine a book that outlined step by step EVERY procedure you could possibly do to a car, from pumping up the tyres to rebuilding an automatic gearbox? It would be a heavy book indeed!
The workshop manual is more a "this is how it is put together" type of book.
It is up to the reader to work out how things work, how to dismantle, how to assess the serviceability of parts, and how to reassemble and finally test the component. This takes some practise, some people have a natural aptitude for reading a manual and translating words into actions, while other people try but never get there.

/end lecture.

It is normal to struggle with the innards of the Magna doors first time you pull one apart. Takes a while to work out how to get in there, what all the bits do, and working out what is not working properly. Spending an hour or so and muttering "wtf is going on here?" is par for the course.
Second time of course, is very much easier.

I'm glad I could help. Lack of detailed information - especially from a 'service' manual - shits me. If I encounter a step in any process that isn't obvious, then I expect to have the information to tell me what is correct. The Magna/Verada service manual is by far the worst i've ever seen. It's borderline useless for many things

I wonder why the unit failed in the first place. Very odd.

Does your fix allow the central locking to still work on the door lock?

Don't expect a workshop manual to have a step-by-step procedure for anything you may need to do to your car. It is not meant to be a "how-to" book. Imagine a book that outlined step by step EVERY procedure you could possibly do to a car, from pumping up the tyres to rebuilding an automatic gearbox? It would be a heavy book indeed!
The workshop manual is more a "this is how it is put together" type of book.
It is up to the reader to work out how things work, how to dismantle, how to assess the serviceability of parts, and how to reassemble and finally test the component. This takes some practise, some people have a natural aptitude for reading a manual and translating words into actions, while other people try but never get there.

/end lecture.

It is normal to struggle with the innards of the Magna doors first time you pull one apart. Takes a while to work out how to get in there, what all the bits do, and working out what is not working properly. Spending an hour or so and muttering "wtf is going on here?" is par for the course.
Second time of course, is very much easier.

It might be normal for you, it's not normal for me. Yes, every 'service manual' for all of the bikes i've worked on will tell you step by step how to dismantle everything, how to dismantle and rebuild a transmission, how to check every component, often they'll even tell you what to watch out for when splitting cases, where to apply force etc. I'm not a car person but my Camry service manual also had a hell of a lot more information than this. The Magna manual is just crap, you may find it fine, but compared to other manufacturers it's ridiculous

And yes everything still works on the door. I don't remember what the inner workings looked like, but I did find some broken plastic. The rubber band is just there to apply a very small amount of force which allows the mechanism to close when the door is shut. The rubber band doesn't experience any force itself when the door is closed, so it's not a stress point. But some slight pressure is required, else it doesn't stay shut. If the rubber band snaps, the door will stay shut until the next time it's opened. So no need to worry about it flying open unexpectedly

Well I just proved my point, rubber band eventually got weak and broke. Door stayed close until it was opened manually then wouldn't shut again. I replaced the rubber band with a 'rap strap'. Should now last a million years

The catch in the door has an over centre spring in it. If this breaks or drops out, you get this problem.
You should be able to see it in action on one of your working doors, by using a screwdriver to trigger the catch.
Perhaps go to a wreckers and get a working one? Fix it properly?