I just got a cover gasket for my 9-bolt differential. It has been weaping oil. The guy at the shop told me to use it combined with some black rtv. I later read on a old post that someone felt this was a mistake, but didn't explain why. Do the two not mix? Any info would be appreciated before I go ahead with it. Thank you.

 

i use high tack or k&w copper in a can on the machined surface and ultra copper or ultra gray on the cover along with the gasket and haven't had any problems. don't over tighten it or you could damage the gasket.

 

I never use a gasket. Only the gray permatex.