Many a rear diff has been sealed with RTV (Ultra Black is what I use), but when a gasket is available, I will use the gasket. I think it cost me $9 (IIRC) at the dealer for the gasket and I ended up with two of them for that price.

 

i work at autozone and i was outside one day and i thought someones car was on fire. turns out this old man had dumped seafoam into his crown vic while it was running. that was when i discovered that seafoam will do that. of course the exaust wasn't leaving as fast as yours did, it was lingering.

 

yea lol i would advise if you want to or need to and have the ability to do so, do it seafoam worked great. As for kyle i will probably head down to the chevy in a couple days get a new cover and gasket