I just replaced the oils seal on my transfer case output shaft. I took the old one out and bought the same one from Napa. The old and new looked identical, but I don't think the old was OEM as it looked like someone had been in there before. This seal is similar to a pinon seal and is pressed into place.

So tell me, what is to keep the oil from leaking out of the mating surface between the outer rim of the seal and the transfer case housing? It is just metal on metal. No gasket, no rubber. I can see how the inner rubber ring of the seal will seal against the flange pinon surface, but it seems to me it could leak outside the seal. I know it presses into place, but how does metal on metal mating surface hold oil?

 

I forget what that seal looks like, but most seals either have a rubber coating on the rim to seal, OR, the rubber part of the seal extends in a disk to cover the inside of the metal part, and when the seal is seated fully, that rubber is pressed up against a ring of metal surrounding the shaft. And that's where it is supposed to seal.

 

Pinion seals are similar. They fit in so tight that no oil will get past. I have seen people put a little rtv on that surface but I think it just gets pushed out and doesn't do anything anyway.