I can help
I did some trouble shooting and have provided the diagram below. That way you don't have to worry about getting to the wire colors. I just watched your videos. Looks like the Up/Down motor is frozen but the Left/Right motors is functioning perfectly. I did several rounds of contact cleaner hoping my motors would free up. I was able to move the motor in a downward motion with more than average force but when I went to pull up on the gimble the teeth on the gimble gear track start breaking off. GRRRR!
Hardway, you need to get all the way down to the motors so you can turn the shafts themselves. Shoot contact cleaner into the motor and on the shaft at both ends. After a day or so, start to rotate the shafts directly, not via the gears, slightly back and forth, then spray in more cleaner.
It's a bit of a chore to get the unit dismantled to this point but like I said, I've freed up four motors in this way. It's certainly easier to find a good mirror but this can work as a last resort.