during the last checks, have you used the handwheel to position the buckets. the reason I asked, I am ASSUMING the motor is bush design and that maybe you burnt one of the commutator's teeth and by manually spinning it to a new tooth would allow it to start.
another test would be check the two leads of the motor for continuaty with the Ohm setting on your DVM. I checked my motor (that had't been spun in decades) and it showed 15 Ohms. after spinning it a little, the DVM became a "random Number generator " and showed about 20 to 30 ohms. A reading of infinity would indicate burnt away brush or tooth