Ravager Diff Oil
#2
They have a paper gasket in the diffs allready so all you would need is the oils and good set of tools to break it down you don't want cheap tools to strip screws.
#3
gasket if taken apart properly will prob be ok. I have nerver heard of one really going bad. You do not need to silicone sealer the pieces together either thats what the gasket is for .make sure you put it back the way it came off and make sure all the gears are all seated.