Go,
Have you found a satisfactory repair to your top problem?
I would think that with a city the size of Dusseldorf, surely there is
a motor rebuilding/rewinding service there.
1. Have you removed the motor and screws from the system and see how
hard the top is to raise by hand? (if that is possible)
2. Have you taken the screws out and see if they are free or just how
much load is required to move them?
3. Are you satisfied that there is no more load on the motor than
necessary to move the top up and down?