As a guy who fixed his broken MR Enterprise, I'm grateful to the many old RPF threads on the topic of stuck nacelle motors. Still, you'd think none of you guys had ever watched Star Trek. I read here of loosening the motor by a light tapping, a back massager or even through the vibration of an electric toothbrush. Jeez - how did James T. Kirk take care of a recalcitrant machine? He didn't give it love taps. Kirk shot out the Trelane's mirror. He blew up the computer on Eminar VII. He smashed Korob's magic wand.
How did I fix my stuck nacelle motor on my MR Enterprise? I beat on the nacelle until pieces flew off. Works fine now.
Actually, after reading the threads here, I got out a small wooden mallet and wrapped the nacelle in a cloth. Then I hit it. And I hit it a few more times. Finally, the nacelle made a slow, quarter turn and then stopped. A few more thunks and it turned a bit more but then stopped for good. A half a dozen extra hits with the mallet did nothing. Channelling my inner Captain Kirk, I told Scotty to fire the Enterprise's phasers at Apollo's temple...err, I really started railing on the nacelle with my hammer...until I hit it so hard that - POOF! - the nacelle cap popped off, along with one of the three little clips that supposedly holds it in place. I could now turn the vanes by hand. Still, it took a few minutes of helping the motor rotate before it would spin freely. I slipped the nacelle cap back in place with a friction fit in case it needs to be fixed again, glued the clip back on and the motor has worked great since. It's been a few weeks now but running the model for a few minutes maybe every other day seems to have solved the problem.
In the future, don't lightly stroke your Enterprise. That's kinky. Instead, ram a doomed starship down the throat of a planet killing machine. That's what Captain Kirk would do.