Back Passenger Door Not Locking/unlocking

[redsox2004]

Hey there all. I have a 2004 GX470 and have been having problems with the back passenger side door lock. When using the key remote lock/unlock the back passenger lock sometimes works, sometimes doesn't...kind of speratic. You can click the "lock" button on the key remote which locks all other doors (however doesn't chirp) and walk around and the back passenger door isn't locked, which you then have to do manually. Same thing with "unlocking" the remote WILL chirp (signally that all doors are unlocked), which is the case with the 1 exception remaining locked. I was thinking the door acuator which is a pain to get to and replace but wanted to see if any others had similar problems in the past and could offer up any alternative remedies to check. Thanks in advance.