I've been in your situation a few times. I've only ever been able to take the pinion nut off with an air impact gun. Once the nut is off, I remove the pinion flange to expose the seal and replace it. I realize the pinion nut is torqued down to set a pinion pre-load but I've got luck so far and haven't had any rearend gear problems with just tightening the nut back up with the same nut. KNOCK ON WOOD!!!
