lock failure

Hi, Hopefully, someone can help me with this. I have a 2008 C Class (W204) and the snib (the button that can be pressed down to lock the door) in the front passenger door is not going up or down when the central locking system is activated. Can someone tell me what is causing this? And...

My 1991 2.6 is starting to experience early lock, or key, failure and I'm aware that the best thing is to replace the barrel now whilst it's functioning or face a world of pain if it fails. Whilst I suspect it's probably the key, and I only have the one, it would make sense to replace the door...

Hi Everyone. I have a recently developed fault which I hope you can help with. When trying to lock the ML, or when the ML tries to safety lock the doors when moving off, all the doors lock successfully except the drivers door. It seems to try and lock, then unlock, retry, unlock then stop...