Stuck Trim and Tilt

[Sugarloafer]

I have a Yamaha F100, and whenever I raise the trim/tilt to the maximum height (motor all the way up), the the engine gets stuck and the trim/tilt won't release to allow the motor to go down. I hear the trim motor run, but something is locked. I don't know if the piston shaft is bent, or there is an air lock in the hydraulic system. To lower the engine, I have to turn the release screw and the motor drops back down. Any ideas? Thanks!