Gary,
The schematic is in the back of the manual, and if you look closely, it includes the rotators. I can send you a copy if needed. I have been looking for a service manual, if one exists, for years, but no luck either. Taking the rotator apart is not difficult as long as you are methodical about it. However, do so above a large pan or bucket. You WILL have some ball bearings fall out. Trust me on this. :)
There is a pretty good selection of tips and comments here: http://webpages.charter.net/k.swaggart/W7KKE/rotor/rotor_help.html
The picture of your problem has changed a bit as more information has been added. I may have misunderstood, but it sounds as if you might have had azimuth problems with the basic unit. If the reference pot, mentioned by another poster, is bad, then it will cause the unit to jump as the value changes suddenly. I had a burned spot in an old Kenpro which did exactly that. Fortunately, it was in the elevation rotator, and at high angle. One thing to check is to put a meter on the output from the DIN connector and watch it as you swing the antenna. There is some damping, and an external meter might be more sensitive to jumps. Basically, work backwards from the antenna controller toward the computer.
Oh yes, if you already have the manual, check the drawing of the pins for the DIN connector. Some, perhaps all of the manuals have a typo. It should read:
3 Connect to Pin 8 to rotate UP 5 Connect to Pin 8 to rotate Down
They are reversed in the manual, though the schematic is correct.
Alan