First off I like to say "I used the search" and found nothing on what gear oil to use when changing it out in the differential. I know I have to use Syn 75W90 I remember reading last time before the thread got deleted that it needs special additives. I wanna put in poyal purple but what else do I need. Oh and I do believe this is the first time it's ever been change in 115K miles. Thanks

 

I use GM Synthetic Gear Lube part # 89021677 and GM Positraction Additive part # 1052358

 

go with Valvoline gear lube and GM additive, the gm grape juice is nearly $30 a quart and that ludicrious