I was a company tech for Photo-me for many years. I can tell you that the transmissions are probably the most Rube Goldberg device in the whole machine. I recommend that you try and contact Photo-me in Texas or one of the other operators out there to see if they will send you a new one or trade out with you. Some common problems that might look like a bad tranny are as follows:
Broken plastic spacer underneath transmission ring.
Pulley slipping on tranny shaft.
You can also sometimes shim up the spider a little if the tranny just lost a tooth ie. is hitting too low to activate trigger.
Also you can tighten the spanner nut on the side of the transmission while it is running to take out left to right slop.
If you contact Photo-me in Texas tell them Zak sent you.