replacing the axle shafts on my 12 bolt tomorrow, and was wondering everyones opinion on the best fluid to use to filler back up again. I was once told there is some kind of additive as well for a posi rear? thanks guys!

I use Valvoline 80-90 non synthetic and Gm posi additive. NEVER a problem.
Theres other oils to decide on, some already have an addititve added


http://www.chevelles.com/forums/showthread.php?t=206672&highlight=posi+gear+oil

http://www.chevelles.com/forums/showthread.php?t=67246&highlight=differential+fluid