My gearbox is shot! The neutral light flashes once every second and the car is very hard to drive. Unfortunately there is no local Magna specialist who can tell me whats wrong with the car, and even if it is repairable. I've been told I need it replaced... but I've also been told that because of the model, I can only replace it with a similar gearbox without an oil filtre (bear with me, I dont know alot about cars, so I'm hoping for a little expert advice), is this right? and if so, will a Magna Executive 2000 gearbox fit my car??

If this happened today, it is likely to be heat related. The same problem happened on one of my cars and it fixed itself.

Flashing light indicates limp mode fro transmission, something made ECU go into limp, can be few things, you really need to get to someone who can diagnose MUTTII, (ECU protocol) so you can see what is causing it. Chances are your transmission is alright.

Check your manual and you'll find that there are two reasons for the flash, one is either due to it overheating or because the computer has a registered a gearbox fault. It all depends on the frequency of the flashes - either one flash or two flashes per second.

Also, if your wavespring does break, you won't have a warning light like that. I believe only if the oil pump breaks then a error is logged.

As for replacing the gearbox, as long as it a 4speed gearbox from a TF-TJ, then it'll bolt up and work fine. You may need to do some slight wiring modifications, but to my knowledge, all 3rd gen V6 gearboxes will clip into your current engine loom and work. There are differences in ratio's between the models and especially between the 3L & 3.5L ones, so try and find a same model gearbox as your current car for the ideal setup.

If you're not confident with replacing a gearbox yourself and need to pay labour, then it might be worth getting a reconditioned one that won't have much risk of failing in the future, instead of a second hand one in unknown condition.