Hi. I have a 2010 A3 and two doors with this problem. I changed one of the lock mechanisms and it solved the issue for me. The other door is on my to do list. The aftermarket part is about £30 on eBay and as someone else stated, you need to strip the door down and get the part number from the faulty one to ensure you get the right one (absolutely necessary - none of the parts dealers had the correct number on file for mine). It’s mostly a straight forward job with one awkward little catch that connects the part to the door handle rod. It was a cold day when I did it which didn’t help.
