When I pull motors apart I clean the insides of the case with denatured alcohol, then clean the commutator with it too. I do not clean the windings with alcohol as that can dissolve the lacquer on the wiring.
Then I put the armature shaft in a drill motor and while the drill is running I clean the commutator with fine sandpaper then wash it down again with alcohol. You can also use electrical parts cleaner if you can find it.
After that I clean the brushes, springs and brush tubes then inspect them. Brushes, springs and brush caps are still available for the FW and other motors so if they look like they're worn over half way replace them.
Then if needed I rewire the motors.
The little felt wic inside the grease tubes are available as is the brushes and springs from Sew-Classic and other places.
The motors are not complicated so generally they're easy to clean and service.
Joe