Switch tested good. Power at the motor. Connectors cleaned and Corrosion-X'd. Turns out it was just the motor binding up. I suspect when I take it apart I will find the shaft lip seal virtually destroyed.
I just re-built the aft toilet and had to replace the seal housing - the white plastic part that attaches to the motor with two screws - because the small shaft lip seal had melted into the plastic assembly and could not be removed in a manner such that a new shaft lip seal would fit in the recess and be water tight. Hopefully I'll be luckier here. Lesson learned: 2 1/2 years is too long to go and 2 years is the very best you're gonna get between rebuilds. From now on I will rebuild every 2 years or less no matter what.
Bill: Thanks for making a trip to your engine room twice to trip and re-set the circuit breaker to verify it powers both motors for its associated head. Wish I'd though of that common sense test.
SM384 Sirena Azul