Driver's door lock mechanism not working

Hello,



I've recently picked up a Laguna II estate (2004) and noticed the driver's door won't lock when using the remote nor when pressing the console button. I only noticed this when randomly checking to see if the car was locked - it was, except the driver's door opened and the alarm went off! All other doors lock fine.



What I've noticed is that the little round override/toggle widget above the lock in the door only moves a tiny amount when trying to lock the door, whereas on the passenger side it moves a good deal.



If I use a screwdriver to turn the toggle, and shut the door and lock, it's fine, all locked, and the remote will successfully unlock the door.



So there's power reaching the lock unit, which tells me the problem is localised to a mechanical fault right inside the lock.



What are the common faults and can I get in there to fix it myself? I'm happy to take the door panel out , but can I get at the lock to remove it ?



Is it serviceable or am I looking to replace it? Presumably it's a common part from a breakers yard.



Thanks, Mike