I have a 2003 Chevy Blazer 4wd with a locking differential. I was hoping of not to start another thread, but the dealer scared me off for what they wanted to charge me for there fluid, and confusion on the web. So this is what I learned and have questions.

-It seems that Eaton G80 are a commonly used locking differential in GM trucks. In the service codes in my glow compartment, G80 is one of the codes listed there. Would that mean I have a Eaton G80 rear differential?

-Owners manual says to use GM part#1052271, do not add Friction Modifier. Boy, that stuff is expensive. Anyone believe you must use that stuff?

-According to my search on the web, there seems hope there is aftermarket solutions, but its confusing to know whats the best option. What is the consensus of what to use?

 

I've been using plain old 80W90 gear oil, your choice on what flavor. Closing in on 240K miles and 14 years of use. And as you have been told, DO NOT USE any type of friction modifiers.

 

Ok, it seems I have learned more. Would anyone know if GM Part#9986115 replaces GM Part#1052271? If so, that is a 75w90 synthetic oil. Also, that GM Part#9985290 would be allowed also by Eaton, which is a mineral 80w90 oil, which maybe why AJBert said in his reply worked.