Well, I guess it's a Swedish Vacuum cleaner motor. I use it for power from my hydro-electric deal I put together. Since it runs 24/7, YES. I've put bearings in it a few times. Once Ice popped off one of the magnets in there. (JB weld to the rescue, (again).

What I'm wondering, thinking...the relative position of the (fixed, permanent magnet"s", that provide the field), could the position of the brushes(/brush holders), relative to the magnets affect the arcing/properties of what's going on at the contact on the commutator.

That's why I asked when you mentioned direction. If it was "biased" or "preferred", one direction, maybe I might get that weirdness going the other way. It might have a "lead" or something.

I DID abandon the original brush holders, (lets say at 9:00 & 12:00), and install new Makita hokders at 3, & 6. Really I'd love to have the whole brush plate so I could rotate it. I'll get right on that!