My EB4424 spindle sander has stopped oscillating and the spindle remains fully extended upward and it sounds like a gear is slipping. I opened up the gear housing and found that the retainer clip on the end of the motor shaft had popped off. I replaced it, reassembled the unit and turned it on. It made one cycle then the same failure occurred but, when I opened the housing again, the circlip was still in place. This is a very easy assembly to access and repair however, I would like some guidance on what part(s) I need to order. I have found a very clear parts digram but am not sure what to replace. I can't see any visual damage. Any help here would be much appreciated.