How hard is it to replace the diff gasket (side the yoke goes into)

I have my trans and DS out, was wondering how hard it would be to replace the gasket that is on the DS side. I took the DS out and i saw it was alittle moist around there and the bottom, any ideas? Could be oil from intake blowing back, hehe.

You mean the pinion seal. It's not hard at all. Just pry it out and install another one, you can use a piece of wood and hammer if you don't have a seal installer. Sometimes they are hard to get out. You can use pretty much anything to get it like a screwdriver, etc. Don't forget that once you take that out the fluid will leak out too, so have some extra handy. Hope this helps.