Hey Wingless! Thanks so much for not only the Welcome but the awesome, quick response! I don't know all of the correct terminology but am pretty sure I understand what you're saying to do.
I can smooth out the outer surface of the commutator. Not exactly sure what I'm looking for regarding clean segment gaps and how to ensure that they're not shorted. Does that just mean that they're not touching each other?
The ends of the original brushes looked pretty good. The brushes themselves were worn short of course but looked okay. The reason I replaced them was that on one of them, the wire that connects the brush to the metal end-cap was broken so I'm sure it wasn't functioning. When I replace them with new brushes, the new ends weren't rounded off to match the curve of the commutator but squared off. Upon a few seconds of running and sparking, now they're broken-off on the ends and jagged. I'm guessing it's a new set of brushes at least that I'm looking at?
Anyway, I'll get that sucker apart and start what you suggested and I'll get some pictures posted as well. Thanks again so much for your help! 🙂