Ok. I took it all apart this weekend and found that the plastic guide that slides on the rail was broken apart and the cable had pulled out. It didn't look like the guide was replacable as there was a large pin riveted to the metal backing plate. I however was not about to part with $130 (plus shipping) for a whole new assembly when the motor/rail/cable was still in good shape.
I found the broken pieces and knew that glue would not do the trick and had another idea. I took the broken piece and drilled a small hole through the plastic parallel with the rail, then mated the two pieces and continued to drill into the plastic still attached to the plate. I also drilled a hole through the face of the broken piece and through the metal plate.
This is the tricky part. I bent the keeper tab out at the pully end of the rail so I could take the cable off the pully and give me some slack. Then I placed the loose end of the cable with spring into the assembly and pulling hard to compress the opposite spring I was able to mate the broken piece with the assambly. I used two #4 wood screws to permantly attach the broken piece into the mating plastic assambly and also into the backing plate. It held, so I slipped the guide back onto the rail, pulled the cable onto the pully and bent the tab back. Works fine.
Here's a picture. I'm sorry it is not in focus. I did not look at the poor result of my digital photography until this morning, long after everything was put together. Here you may be able to make out the screw going through the backing plate and the head of the screw going into the other half of the guide. Don't they make replacement parts for these?