1998 BMW 323 Rear Brake Light

My rear driver side brake light doesn't work on a sporadic basis and I get the brake code on the onboard computer display. I have had it to the dealer, my own mechanic, and have cleaned all of the contacts and connections, changed bulbs, all to no avail. The dealer and my mechanic have "fixed" it and it worked for about an hour or so both times before it started happening again. I have read that this is a common problem on this model but I can't get this common problem to go away. It only happens on the driver side, never on the passenger side. Thanks for your help in advance.