I'm pretty sure each of your slides has two motors turning worm shafts that bring the slide out and back in. I also think that one motor is running but not turning its shaft due to a drive pin or gearbox problem. That's the motor you hear running. The other motor is either dead, or can't move the slide on its own because it can't handle the job by itself. Or the slide goes to move and jams because only one motor is working.
That's based on what you've said, what I've looked up and read, and a conversation with another Winnie Class C owner. About all I can do from here.
Can you get access to it (the two motors), see what's running and what's not? Get a couple pix and either post them or send them to me.