Back door not responding to remote

The back door has stopped responding to the remote. So it has to be unlocked by crawling inside and flipping the lock open manually with a flat screwdriver. This is the second time it has done this. Previously, all I had to do was grease the mechanism, but now there is not even a clunk sound from the actuator. All the other four doors work with the remote. As far as I can gather, all five door actuators are fed from the same location on the master control module. Only thing I can think of is poor ground or broken wire or connection. Suggestions?