Also check the motor couplings. The little grub screw that secures the shaft could be slipping. Also does the motor sound nice and smooth with an even soft ticking sound? If not you could have a "2-phasing" problem where the motor will appear to run normally, but will often drop a pole switch & slow down. Is the mount running too fast or too slow? Too slow could indicate gear slipping or a motor problem. Another thing to try would be to swap the RA & DEC motors and see if that helps.
If you know anyone with another control box, try that. Process of elimination should eventually get you there!
Good luck...
