The new information of the hot motor makes me also suspect the motor is failing. Perhaps it would be best to put the spare motor in and send the old one old to be rewound.
I don't necessarily agree. Motor shops don't usually don't have the same variety of materials or capability as a production facility. Its harder to tightly fit thicker winding on a premium efficiency motors and often are often less efficient than factory specs.
There was a study somewhere that compared new premium efficiency vs rewound one. The latter did not score as well on an efficiency test.