If the cables are chewed, the gear will spin... and the cables will just sit there staring at the teeth wiggling by on the motor shaft. And the panel will also remain where it is. IOW the cables must be intact for the thing to work.
I would suggest checking the operation of the glass, sliding back and forth manually to see how difficult it is. It should not bind in any particular position, but should slide pretty easily from full closed to full open and back to full closed. If it binds, it is either damaged, rusty, twisted, or in need of lubrication. I think you should be able to see the areas where the panel rests on the tracks, which would be a good area to apply some lubrication. Generally a light (lithium?) white grease is smeared using something similar to a paintbrush at the factory. You can use fingers, 'acid brush', or a small paintbrush to duplicate. I would clear the tracks prior to adding just so the application is sort of equal across the surface.