Driver's side lock "sticking" (126)
 

Hello all,
Ever since I bought my car 5 years ago (1987 560SEL) there has been a minor problem with the driver's side door lock. Usually after I close the door I have to turn the key to the "unlock" position until it clicks before I can lock the door. This was never much of a problem, since the key was in the lock anyway, but I recently installed a keyless entry system. Now I have wait for the locks to go down and make sure the driver's side locks as well, if not, I need to put in the key, unlock and then lock. The problem is caused when I close the door only (once the door is closed I can lock and unlock all doors to my hearts content without the sticking problem). I am guessing that this issue has something to do with the mechanism which prevents the door from locking when open, though I am not positive. Any ideas on where to start looking or what might be the problem??