nojelo

I'm losing sleep over this.I have a 2005 A6 and after I'm driving a while and its warm outside the cluster gives a warning brake tail failure and the whole left tailight goes out. If i turn the car on and off it works again.I took the whole tailight out hooked it up to a battery charger for 3 hrs with an electric heater nearby, thinking its something on the circuit board for the led's (which is not servicable.) No failures outside the car. Put it back in and it was cold outside for 3 weeks no problem. Last saturday it was 70+ degrees and sure enough it happened again.Thank you now if anyone can help