[Stocker]

^^ Andy beat me to the punch with that Permatex. It's called Gasket Maker but I smear a thin coating on both sides of a gasket. No leaks, great stuff, made to use with gear oil.

I typically use Mobil-1 75W-90 synthetic, but any good gear oil will work fine. If you have an open diff you don't need any additives.

I'd get 3 quarts and you'll probably have some left over.