Joe,
the problem with the Buhler motor is access. While the very early motors may be dismantled (brushes replaced insitu and commutator cleaned), the later ones are basically throwaway items, although some have had success with overhauling them. The main issue is removing the worm gear from the brush end to enable the end cover to be removed to gain access to the commutator for cleaning. Sometimes the worm gear may be simply drifted off the shaft, but I have been told that heat may be required, but given the proximity to the commutator/end cap bearing, I am reluctant to apply any heat to loosen the worm gear.
I have 'successfully' restored three motors by simply liberally dousing them in a cleaning solution. Preferably some sort of electrical cleaning solvent would be preferable to spray into the motor, but in my case I simply sprayed WD40 onto the commutator/brush assemblies in an attempt to clean them. It takes a few tries but eventually will clean the motor. WD40 is not a preferred cleaning solvent but given that the motos were initially toast I had little to lose.