I had the same problem and I just fixed it. When you try to unlock the door from the inside, the rocker button pushes against a long linkage that pushes against the lock mechanism by the door strike, which is supposed to pivot and push upward against another linkage, which is supposed to rotate the door key tumbler. The problem isn't lubrication, although that helps. Nor is the problem a linkage that is too short. The problem is that, after time and usage, some slop develops in the plastic connectors and, in particular, the one that connects the lock mechanism by the door strike and the door key tumbler. The slop allows this upper linkage to move (down and left) to a position such that pushing the linkage just pushes against the tumbler rather than exerting a torque that will turn the tumbler. You can verify this by pulling the door panel off, locking the door, and pushing against the rocker button to try to unlock the door. With pressure on the rocker button, push the upper linkage upward and to the right--the linkage will snap upward and the door will unlock. The solution is to keep the upper linkage from getting out of position. I did this by unhooking the linkage at it's bottom end, sliding a small spring over it, and attaching the other end of the spring to a small hole I drilled in the door. The spring exerts a small pull up and to the right and keeps the linkage in it's proper position. I'm sure there are other ways to keep that linkage in position, but this one worked for me. Now my door lock works perfectly.