OUCH! OUCH !
I haven't worked on your model of coach , but 10 hours to replace a slide motor. It would only take that long if the slide needed to come out ; that I doubt.
Any slide drive motor I've worked on is reversible , so reverse polarity of the battery wouldn't do a thing to the motor. Slide control module maybe but not the motor.
JMHO: Get the unit out of that shop, and look into the problem yourself, I've got a bad feeling about those guys.