I had to do some rear end work a week or so ago, and I had to replace the rear end gear oil/lube. At the time, all that was available to me was Quaker State 80W-90 GL-5 Synthetic for Limited Slip Rear Ends. I went to the dearlership today and they wanted $27 per quart of the GM stuff that the manual recomends. Mobile 1 was only $7 per quart. Do I really have to put the GM oil in there, and does anybody know why GM oil is so expensive?

 

I am no expert on this but I think you can use any gear lube you want as long as it meets the viscosity and weight ratings the manual calls for. I do believe that gm has an additive you have to put into the fluid because of the limited slip diff. May want to check with the service department for a definate answer.

 

I got Red Line 75w-90 for my rear end. It was about $8 for a quart and already has the additive

 

What you put in there shold be just fine and beings that it says for LS differentials you shouldn't even have to add the Gm posi additive.