Thanks for the info Dojj! The N/S/R door lock doesn't move at all, regadless of weather you are locking or unlocking with the remote, or the key in the drivers door. The only way to lock or unlock it is manually operating the lock from inside the car. If I leave the rear door unlocked then lock with the key, the other 3 doors will lock ok without pinging open, but the N/S/R door stays unlocked.

I've ordered a new rear door latch from ebay, I'll get that on and go from there