i have the same problem, a little hole in the case.. i filled it up and it leaked out within a month, only while driving, so i cleaned the surface around the hole and sealed it with "chemical metal" it was OK for a week but now i see that it's leaking again, so i wonder if ther's any pressure behind this hole? is there an oil pump there that builds up pressure?
and what does a new rear case casting cost? is it possible to replace without taking down the transfer case from the truck?