hi mate, id take the door card off and have a look in the door, check the rod hasnt come of its clip going to the lock, while your there pull and push the rod to the central locking motor and see if it operates alright.
does it unlock ok from the passinger side? if its the lock thats worn you can change over the one from the passinger side, you just need to remove a cir-clip and swap the back part around.
hope this helps mate.