I am having a problem with my Jobo. With my expert drum attached the drive gear that goes onto the shaft coming out of the Jobo will start slipping and the drum will stop turning although the shaft is still turning. The gear is held on with a screw that goes through a brass bushing inside the gear. I don’t understand how how tightening the screw makes the bushing tighter on the shaft but I have tightened the screw as much as I can and it still slips. Do I need a new gear or am I doing something wrong?