So just finally put fluid in on my long term project and its leaking out, looks like between the case halves. Guess its coming out again. What do I seal case halves with, just RTV?

 

Yes.

 

Only RTV I use is Permatex Ultra Grey.
What you're sealing has to be perfectly clean.
Works great then. Have not had a leak in a couple of decades and I own an automotive shop.
I do not trust anything but the "Grey".

 

+1 to what technicalninja said. Anytime I use RTV, it's typically Permatex Ultra Grey or Hondabond if i'm feeling fancy.

 

I used loctite 5699 RTV. When you open up the diff, make sure the baffle that goes around the breather plug on the top is in place.