I have a demonstration to do tomorrow and I would appreciate any help the forum can offer - after a few hours of driving a fairly stiff 19mm Leica R Duclos modded lens my motor is slipping. When resistance comes up to moderate (applying hand pressure, and not too much at that) the gear stops and a buzzing sound comes from the section of the motor under the label (the graphic side decal). It's strange because there's all the resistance in the world when I try to move the gear by hand, but when the motor is moving it is easy halted. It's as though the threshold has been reduced in the motor (I don't know how electric motors work). Any help would be gold. Thank you.