Had no buildup and the brushes look great. I used the wrong terminology previously... meant to say that the windings were all clean. The commutator, however, was a little darkened: I lightly sanded.
Really nothing stands out as being questionable, other than the solenoid plunger and the hole it goes in seemed to be a bit crusty (weired coating, kind of rust colored) and slightly scraped.
Rich, I have no idea how old this thing is. It's a ("Bosch SR0408X") re-manufactured unit. Came with/in the car when we bought the car in late 2015.
Probably order bushings, solenoid and brushes. Install the solenoid and brushes (brushes because they're only about $14 and I've got things apart), but don't want to mess with the bushings unless they're really needed. Be nice to know what the acceptable tolerances are for the bushings.
Would brake grease be good? Has graphite and won't get gummy (and can handle heat).