May not be the right answer, but i had this problem on a clio i owned. Basically ended up removing the door cars and taking out the lock mechinism. Used about half a can of WD40 on the locks and it about fixed it. Just kept opening and shutting the lock with the key, whilst drenching it with WD40. Worked a treat and fixed the seized parts. Cheap fix and you can't really go too far wrong, worth a bash.