If changing the gaskets on the rocker cover of a 3.5 litre , after pulling off all the injection stuff , do you need gaskets for replacing the fuel injection unit. Not game enough to touch it just yet. Is there any special way to approach this job.

You don't need to remove the injector stuff, just the plenum chamber. The throttle body can stay in place, it's supported by a bracket up the back. New gaskets at the plenum/manifold and plenum/throttle-body interfaces are a good idea. You'll want a torque wrench for reassembly, 18 or 19Nm for most of the bolts from memory (check this, don't trust my memory!).

Yep, no need to touch injectors. Just unbolt the manifold and you have access. I leave the manifold attached the the throttle body and just unbolt the bracket at the back of the throttle body, leaving all the vaccuum hoses etc. intact. The whole manifold and throttle body assembly lifts off and there should be enough give in the cables to have access. Just be careful and tie the assembly to the side. I find this method quicker than having to disconnect anything from the throttle body.

Whilst you've got access, you may consider changing the spark plugs as well if they are due soon.

Yep, I've not done it that way before but sounds reasonable, so long as it's not placing undue stress on cables, hoses, snorkel etc.. Leaving the TB in place only requires the removal of the snorkel (2 clips, 1 phillips, 1 hose) and the four bolts between the TB and the plenum, and the 3 or 4 vac hoses to the TB/plenum depending on the model. It does also require the disconnection of the throttle cable from the plenum requiring adjustment on re-fitting but that's no biggie. It's also an opportunity to have a good look in the plenum and the TB to see if it's getting filthy again (usually that's a yes) and clean up if needed (usually it's needed!).

Thanks guys. I might give it a go as soon as the weather clears up, instead of paying to have it done.
Will replace all plugs while in bits. Car has travelled 210000 ks so could do with new ones.
Cars been running fine except for leaking oil.