I'll try to keep this as brief as possible.

2008 Audi S4 Avant, 96,000 miles, no accidents, no major issues

- right rear brake light bulb goes out, according to sensor
- remove r.r. Lamp module, replace bulb, even though it looks OK.
- reinstall
- all lamps in module, including back up light, are now out with sensors indicating same on dash display
- remove lamp module again, carefully inspect
- wires from grommet to multipin plug appear fine, no wear or bare areas or insulation cracking that I can see
- both contacts (multipin plug and receptacle on lamp module) have slight brown discoloring around the brown wire (hot?) pins (heating due to corrosion?)
- used very fine file to clean contacts
- reassembled module
- worked fine for 2 days, then r.r. brake light and r.r. turn signal bulb sensors activated...neither of bulbs would light
- removed lamp module, cut hot wire from multiple plug, fed it through small hole in plastic module lamp chassis and soldered it directly to the hot side of the metal chassis on the module.
- tested before reassembly and all bulbs worked, no sensors triggered
- reinstalled module
- r.r. bulb sensor and r.r. turn signal sensor came on again
- removed lamp module again, checked solder joint (I cannot pull it loose) switched bulbs around, cleaned contacts on bulbs
- all bulbs work, just none work in brake light socket
- gave up and settled for just having turn signal and reinstalled everything
- everything worked!
- just went out to use car and r.r. brake light and r.r. turn signal show bad again
- pulled out of driveway to go to store and within a block, all errors cleared and turn signal cycled normally
- before I got to store, r.r. brake light bulb sensor came on but signal still worked
- came out of store, now r.r. brake light and r.r. turn signal are out again

I know if I take it to Audi they're just going to yank the entire wiring harness for that side and replace the whole lamp module and charge an arm and a leg.

Before I do that, is there ANYTHING that I've overlooked with this?

Edit: I did have it into a shop where both exhaust clamps were replaced after the band holding one rusted through (see previous thread where I though it was flex joints). Does wiring from the lamps run near enough to any of that that it could have been pinched or crushed while work was being done?