After reading all the threads about the rear differentials being a quart low, I decided to check mine last night and sure enough, it was low. I went a bought a quart of Coastal SAE 75w90 gear oil (which isn't synthetic). This oil meets the following specs: MIL-L-2105E and API GL-5. I added the whole quart. Is this oil OK to run in my rear diff. If not, please tell me why. My concern was that the manual called for synthetic and this wasn't. However, the bottle stated it complied with General Motors specs.

Here's a link to the product I used:

http://www.warrenunilube.com/gearoils.html

it needs to be synthetic. I would drain it all out and start over with moble 1 or the like.

Amsoil!!

I drained it out completely and went with Mobil 1 Synthetic 75W90.

x-2, front & rear...:agreed: :grd: