Hi Don,
I had the same problem with my AMI Rowe R90 jukebox and I tried everything; all kinds of adjustments and even replacing optical sensor and the sprag gears. Nothing solved the problem.
I was all set to replace the gearbox with a spare and noticed when spun with fingers, the replacement gear box spun more freely than the original.
I opened the gearbox from the problem juke and found the old grease was thick and hardened. I cleaned out the old grease and replaced it with fresh automobile grease and put everything back together.
The first time I selected a record it chose the correct one and has performed flawlessly ever since.
Good Luck,
Stingman