So I got the new 3.91 open diff (Aka tyre shredder! ) from a 735i today.

Looks in pretty good condition - the oil came out pretty clean too which is a good sign. I'm hoping to get it in next weekend, so ordering new hardware/seals etc this week.

Question's:

1. What diff fluid should I use? After looking through the archives Redline seems to be the #1 choice, however it seems this is less readily available in the UK. I contemplated buying some Castrol (semi-synthetic) 75w90 today but thought I'd check first. If my best choice is go to the dealer I'll do that.

2. How much fluid will I need? (I searched extensively on this but absolutely no clue on any thread I found and the haynes is eluding me)

3. What should I renew... I'm thinking new bolts for the flanges... #6 in this diagram.
http://www.realoem.com/bmw/showparts...73&hg=33&fg=10

4. I plan to keep it for a little while to ensure the 3.91 works out, but is my 3.64LSD worth a shiny penny? If/when I sell it how much should I be looking for bearing in mind it's in absolutely perfect working order?!

Thanks... I'll keep updating this thread and get some pics of the swap when i do it!