The physical lock cylinder or the door handle? I don't remember if your car has a lock cylinder on that side. If it's the door handle-lock plunger thingy, I would think that it's a mechanical problem or a problem with the door module. Here are some places to start. You would have to remove the door skin (card) to take a look. http://www.myturbodiesel.com/1000q/a4/door-card-removal.htm
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