Q7 Tailgate indicating open when closed problems

My tailgate is operated several times a day as I use the car to take my dog out for his twice daily walks. A couple of years ago the latch actuator failed (which could be heard by the slipping of the plastic gearwheel inside the unit) and the alarm on the dash indicated that the tailgate was not closed when it was. This was because the actuator was not pulling the tailgate latch into the the two microswitches G525 and G526 which are the closed senders. I replaced the actuator and all was find until today when the actuator failed again (same problem with the destroyed teeth on the internal gearwheel - why make it plastic when it carries a large loading). However the dash still indicates that the tailgate is still open even though it is closed and the actuator has pulled it into the two closed sender microswitches. I thus assumed that the microswitches may be faulty so these have been replaced also but the problem is intermittently indicating the tailgate is open. Can anyone suggest why this is other than that the the convenience system central control unit 2 J773 is at fault.

The other situation this causes is that the if the central control unit J393 is told that the tailgate is not closed (via the two microswitches and control unit 2 J773) then it does not activate the main brake lights, tail lights and indicator lights on the tailgate but activates the brake lights, tail lights and indicator lights on the rear bumper. 

Please help as it is disconcerting when driving with my dog in the back.