2002 Audi A4 3.0

I have had this issue for the past 10 years. The rear light bulbs, usually the break lights and/or left turning light will keep going off. And it usually happens when I have the car on park and reverse. Initially, I thought the bulbs had died, but it looks more like a bad connection somewhere. The light bulbs are all in good condition, there is no visible rust inside the holder, and I even replaced the entire holder with a used one I got from ebay and the issue still remains. One thing that is consistent however is that that it is usually the reverse position that triggers it, the light bulbs are always in good condition, and once i take it out and put them back in again, they work great for a few weeks or months. Then the cycle repeats. Can someone help me understand what is happening here?