I would think any good GL5 spec 80w140 fully synthetic oil should be good. There are no parts for the sulphur to attack. I actually think it's a Hypoid not a bevel so the shear is even higher. I just switched to redline 80w140 GL5. The knocking when you go over a bump on light load is the backlash in the bevel gear and is normal. As the swing arm comes up it unloads the output of the box as the two share the same centre point and then it clanks when the load comes back on. Good luck
Thanks for that info. I was guessing that either the bevel box was loose or my rear wheel bearings were on the way out. I have a spare set of high load FAG bearings in the cupboard just in case to replace the standard NSK ones if they do go. The car had been in storage in the UK over the winter and someone had pumped the rear tyre up to 40 psi. Once I reduced it to the correct 25 psi, the clanking was nothing like as bad. As I don't do long journeys in the M3W, I can live with the whine but as it is going into Esprit anyway, it would be easy to change the box oil. I thought I had a couple of litre bottles of 85W-140 Syntrax in my French house but they must have gone back to the UK in the truck with the 911 RSR. I have a very good Motul supplier who I got some 20W-60 Le Mans synthetic oil for the engine last week and I am sure they will carry a GL5 Motul gear oil.
