2009 driver's power door lock
 

All the power locks work except the driver's door. Pressing the lock button operates all the locks except the driver's. The keyless entry operates all but the driver's lock. The driver's lock can be operated manually and by the key lock. On rare occasions the driver's lock magically works. I assume it is the actuator, but wanted to know if there may be another cause to rule out before buying a new one, installing it, and then finding out that I should have checked something else first. The least expensive replacement is $173 on Rock Auto. Thanks.