I've only done a very few pinion seal changes that didn't end up also involving changing at least one bearing, either immediately, or after only a few miles of running on the new seal. The reason a seal starts leaking is usually looseness in the bearing that allows the pinion flange to wobble and damage the seal surface. Getting the preload right on a used bearing can also be a challenge when retightening the pinion nut.
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!