When you make the checking bearings, just make sure to do it slowly and try hard to keep the inside of the bearing round.
Grind lightly and evenly, then try to slide it on the pinion. If it doesn't slide on, repeat. Only go far enough that it slides on by hand, but without being any kind of loose.
I hold the bearing cage, so that the inner part of the bearing can spin freely.
Then I use a die grinder with a cylinder stone on it, and apply it lightly and flat as humanly possible, to the inside of the bearing.
The rotation of the stone will drive the inner portion of the bearing to spin, hopefully keeping it round.
Just go slow and don't use too much pressure, or allow the stone to stay in one place. You don't want flat spots or distortion (egg shape).