Agree with all Slobs advice. With the starter out it may be worth cleaning the commutator with some 800 grit wet and dry (cleaning any abrasive off afterwards with brake cleaner and /or airline) and checking the continuity across the poles on the commutator. I do not know how to check /test the field windings in the motor case, doubtless someone will be along to let you know how or just google it.
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