golf 91 jammed door

What I've seen happen on the rear doors is a small part in the lock that flips or flops when you operate the lock button getts dirty and corroded and the spring that detents it one way or the other does not do the job. What I've done is to look at the other door lock then spray wd40 or your favorite penertrating oil in the crack between the door and body and work the button vigorously up and down and at one point you will notice a different feel and it will be unlocked. Open the door, remove the lock mechanism and then clean and lubricate it properly.