Did you set the proper preload on the bearing? Seals leak because the shaft or yoke they're riding on is so wobbly the seal lip can't keep up with the movement. You've probably got one or more bad bearings in the mix or the pinion nut hasn't been tightened properly to preload the tapered roller bearings.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!