If the motor turns freely w/no load, but stops w/some load, I'm still suspecting something frozen up.
Is the ACME nut frozen? Never heard of that, but its possible. The motor has a resistance shutdown feature, such that when it hits physical limits requiring torque above some amount, it shuts itself off. This is in lieu of a setup w/limit switches.
Never heard of anyone taking the motor head apart, short of a collision or tow truck oopsie. But there's always a pioneer out there waiting to explore. Maybe that's you.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project