I had the same issue, and there are several things. First, the motor could be stripping the gear inside. If this is the case, and worst of all, you need to buy a new motor. 2nd, there is coupler attached that could be getting worn out, the large plastic ring attached to the motor and shaft. Sometimes this gets worn out, and needs to be replaced, which is expensive. 3rd, there are 2 metal plates inside that coupler, and these over time will develop a groove from being spun so much, and the rod will keep spinning until sometimes it grabs. You can try to remove those and turn them over so the outside of each plate is now on the inside. Lastly, and back to the motor, the end of the motor where it connects to the couple, there is a little nub, and this gets worn down over time from spinning, and cant quite connect correctly, and this also requires buying a a new motor.

Looking at the video, I would suggest its the last issue, with the nub being worn out. These motors are built so they cant be taking apart, unless you really know how to. One last thing though, check the wires going from back of balrog, make sure they arent getting hung up.