Although my central locking was still working, i also lost the passenger front door locking a couple weeks ago.
So i bought a second hand c/locking motor/lock,swapped it out and its been fine since :dance:
When i took the old one apart, the motor had seized solid !!
I have exactly the same problem, I replaced the door lock with a 2nd hand unit which worked fine for a bout a month and now the problem is back again. A good tip to check the motor, I'll do that as everything else in the lock assembly looks perfect.
My passenger door and rear hatch stopped locking also. there is an out station in passenger door that sends power to rear hatch button. wire had come loose in door and window cut it when lowered. I spliced wire back together and that fixed door and hatch lock problem. Hope this helps.