I had leaks when I had stock sealed bearings and separate oil seals because the axle housing was messed up a bit when it was narrowed. I threw out the oil seals and used the Currie bearings with O-rings. No more leaks. I haven't used a standard oil seal on any of my last three projects with 9" diffs.

If the Mosers have O-rings, I guess you could install the oil seals also, although I never have. Double protection?