I just wanted to reply to this one since it's the one that comes up even when looking for a mk2 4x4 gearbox and diff oil change on Google.
There is actually a diff fill plug but it's not easy to get to on the mk2, not sure if that's different to the mk1?. I drained mine and luckily checked if it had filled the diff after running which it hadn't. I needed to undo a 5mm Allen bolt at the top back and fill the diff with a syringe where it took about 600ml.
So in short. If you've got a mk2 4x4 pre fl and you drain the diff oil, make sure you refill it. It doesn't fill from the gearbox!
Cheers
Callum
