As per subject, I have a 1997 UK Turbo. I'm planning to do a diff oil change, and I have a few questions:

1. The workshop manual recommends 80W-90 oil for the rear diff, however other sources recommend 75W-90. What would be the best grade to use? I was thinking of using Redline Lightweight Shockproof 75W-90.

2. Probably a very silly question: I'm assuming the front diff is located in the gearbox and uses the same oil, i.e. I change the gearbox oil only? Apologies, but I've just bought the car and I'm not familiar with scoobys (yet!).

3. For the rear diff, the workshop manual recommends three bond 1205 packing fluid. Is this correct, or should I use some kind of gasket?

4. Can anybody recommend a place to buy the sealing gasket for the gearbox drain plug? Is it a dealership-only part?

Apologies for the rather simplistic questions, any advice much appreciated.