sounds like a bad sensor that is near the "master gate". Do you know how to test a sensor?
Im gathering the diagrams of sensor that should be checked. Any component can go bad overtime. There isnt anyone cause beside the abvious of sensor being hit during replacment ofa part. Pulling paper out from that area impoperly. Heat and cooling cycle it endures overtime etc.
Master position sensor is most likely bad. Your repair person should be able to test if its open