Felpro makes a gasket, you can buy it at any autozone. I have the number written down at home. Gaskets and spark plugs and such are the only thing I buy at autozone.
I always use the fiber gaskets and never ever ever had a leak on any rear dif this includes offroad vehicles. The best part is the next time you take the cover off you don't have to scrape everything. I think the guys who have leaks using them have covers that are bent. Some of the dana difs came factory with silicone.
FEL-PRO Part # RDS550281 $2.35 on rockauto.com