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If you think it's worth your time and expense, Turn the Commutator and replaces the Brush's and Bearings.
Turning the Commutator requires removing the Armature and machining the Commutator (you'll need access to a small Bench Lathe).
After that you can take an old Hack saw blade (grind the set off the teeth) and use it to cut the mica between the bars down a little. Smooth with non-conductive emery paper.
If the rest of the machine is sound (right angle gear head & frame) it should work as good as new.