On assemblies that don't need routine assembly/reassembly, like the differential carrier, I would recommend Permatex "Right Stuff". Stupid name, great sealant. It is a rubber type product, no need for gasket. The only downside is it also has moderate adhesive qualities.
I used it for the differential carrier of my '50 COE five years ago where I could not find a gasket and hard to cut your own on something that big. Not even a seep so far. I understand some large equipment manufacturers use it OEM on things like oil pans and use it without gaskets.
Kent
