Using GRG's pic of the internal wiring of the switch
If you are going to do a repair and open it up, note how the belt on/off slide switches one side of the AC power...but the eject button switches the other side of the AC power! Fascinating.
The parts lists for the milk depot show so gear motor mechanisms that appear to use DC can motors. So somewhere inside are some diodes. Since it apparently operates up to 14V AC, I'd take a 9V battery and briefly power the eject DC motor itself.
If the motor jerks but no eject cycle, then a mechanical jam. If the motor spins then I'd look for a loose wire or mechanical adjustment to a cycle-limit switch that cuts power to the motor after each can goes out. In the video above, you can see a consistent "hiccup" in the man's motion at the end of each cycle.