Errything's back together. Bed back on, 'new' hitch on, albeit without the 2 bolts that go into the bumper (those holes weren't being used with the old hitch, so the threads are a bit crusty). I put 2qts of Royal Purple in the diff, and drove around for a bit, and nothing's leaking out (RTV, paper gasket, and more RTV should hold up well, I'd think?

).
Ok, now huddle up kids, it's story time.
Once upon a time, there was a diff cover, with what appeared to be some gear oil on the outside.
How could that happen? A crack you say?
Lets see what's on the inside.
Looks fine to me.

Maybe we should hit the diff cover with a screw driver and see what happens. OH MY!
Well, there's no crack, looks like it was just in the paint.
Wait, what's that? Is that an itty bitty hole is see?
Yes, yes I think it is.
Lets poke it with a screw driver to be sure.
Woah, that's definitely a hole! Lets poke it a little harder.
Uhoh....
The end.