I seem to have a leak from the mating surface to the tranny when I park uphill, but it is nearly gone when I park on a down grade. Is this typical, what can I do to fix it.

 

How bad of a leak? I've heard that with older trucks, the metal can actually become slightly porous allow a little risidual, but it wouldn't be anything major.

 

The Toyota orange RTV worked wonders for me when I built my motor/installed the bell housing on my 6 speed tranny

 

that section isn't normally filled with oil, and isn't meant to hold it...your tranny output shaft seal is probably leaking....with the transfer case out it's pretty easy to pop out etc because the input for the TC is actually the part that the seal rides on, leaving a gap between the tranny output shaft and the seal.