Good hints, thank you. I've now determined the motor is working exactly as it should, the cam is properly positioned, and when turning the power off, the motor "bumps" (turns slightly) such that the cam moves and the flat spot clears the "front/back" pin. The pin is not bent.
The issue is that the panel does not slide forward via spring action as it should. It can be moved by hand, but over time it slowly retracts to the "on" position even though the power is off.
The spring/cord/flywheel assembly on the side nearest the center of the receiver appears to serve only as a damper so the panel slides smoothly to the "off" position instead of snapping into place.
What I don't understand is what causes the force that moves the panel to the "off" position? The large spring surrounding the piston has a set screw but I do not see where this should be adjusted. I've tried both extremes and if adjusted toward the back of the chassis it prevents the panel moving forward at all. When adjusted toward the front it even more quickly slides the panel to the "on" position when the power is off.
Note the cam in the "off" position has no contact with the front/back pin. The panel is free to move forward and back. Do you know if that's the correct position of the cam?
Suggestions appreciated on this mechanical puzzle!