The quick and dirty runout test is the magic marker-- take the head off and run the mains up to a moderate speed (doesn't have to be too great), then take a sharpie or similar and bring it slowly to the side of the shaft near the end. Take it away quickly when it brushes the shaft, then turn off the motor. If you have a line all the way around the shaft, there's no runout worth mentioning, but if you have a shorter dash, then the shaft is bent toward the center of the dash.

All that said, if you take the head off and spin the motor up a bit, and you can't see any runout, then you probably don't need to worry about it anyway .