The fluid in my M5OD and rear diff have never been changed. 17+ years old and over 400k miles, I'm thinking about doing it for peace of mind. Are there any preferred lubricants for this? Is Royal Purple as good as everyone makes it out to be? I have a 3.55 non-LSD rear.

 

M5OD: Any Mercon V ATF, full synthetic preferred.

Diff: Any full synthetic 75W140.

Whatever brand Walmart has. Supertech is fine.

 

Bookmark this, it goes back about 10 years worth of models:

https://www.fcsdchemicalsandlubrican...n/quickref.asp

 

Tip - make sure you can get the fill plugs loose before you drain them.

The factory only uses RTV on the diff cover, which has to be removed to drain it. Autozone has gaskets for the 8.8 if you would rather use one instead of RTV. I use both - a gasket and a thin skim of RTV on both sides.

This makes the fill a lot easier:

http://www.harborfreight.com/oil-suction-gun-95468.html