Another tip for your carbon brushes.
If or when you remove them for inspection, like to see if the wear patter is across the full face, you must put them back in the same holder and in the same orientation. If you put them in different they will have to reseat due to manufacturing tolerances having them not exactly in the same spot relative to the com. It is not a lot, but if you turn a brush around and run the motor for a couple minutes and pull the brush back out you will be able to see that only a very narrow area is actually making contact with the com.
Any time you are running the motor with less than full contact the amps per sq in go way up and you are stressing and heating the armature, it will not show up right away, but it will reduce ultimate service life.
We once tested some motors. Run at full load with proper breaking of the carbon vs run like a customer would by just slapping in new brushes and going back to work with no break in time. On average the motors that had proper carbon break in had an ultimate service life that was about 15% longer.
There is a lot more science in carbon brushes than most people realize.