In your case, 91W350, I wonder if the gearheads on here might say that your pto back lash is too tight. Just a thought but it sounds like the gears are turning with more force than the drive shaft friction (winch internal gears) can stop. Also the (drive shaft friction), you are probably spinning the worm gear, main gear, and winch drum shaft all the time if you say the drive shaft is always turning. You could probably stop it by engaging the winch clutch handle, but I wouldn't recomend doing that, if the pto is bumped then she could fully engage and cause a mishap. I would try to make this stop, I wonder if the shaft was removed if the flange on the pto would be spinning faster and harder.