Good question... I put Royal Purple 75W-140 in mine, no problems. (yet?) GM 12-bolt, Richmond 4.56:1 gear, GM Positraction, Moser C-Clip Eliminator, Moser rear girdle.
I rember coming across the same question several months ago for a customer and I found some information that led me to believe the synthetic gear lube was ok. Perhaps it was the API rating? I will check back in my notes and see if I can find it. :D G r a n i t e C i t y P e r f o r m a n c e custom engineered competition components ---- Bob Haggard <[EMAIL PROTECTED]> wrote: ============= I have a new 12-bolt from Moser Engineering that I installed last month and the paperwork that came with it states in CAPITAL PRINT not to use synthetic lube. I believe that EATON says the same thing about their posi unit. I called to tell them I have a pinion seal leaking and asked about synthetic and was told that I can change it later on after breakin but the sales rep didn't know how long I should wait, any opinions???? Bob Haggard
