My left tail light has moisture behind the lens. Odd as this is a no paintwork car, so it’s not like it was out for a collision or paint repair and the seal was compromised.
Have others with this chassis encountered such? If so, what was the source and what was your remedy? Left side marker too, but that I’m just waiting to swap out with smoked lenses so don’t care right now.
Suggestions / insight appreciated - thanks in advance gents!
Remove the light, dry it out entirely, make sure there’s no moisture in your trunk/spare tire well, re-seal, re-install.
I had this problem a while ago and those nice people at Audi replaced it FOC as a warranty / goodwill item, maybe try asking an Audi dealer they might replace yours too?
This was a very common problem on the C6 A6s. I remember replacing a bunch of tail light housings because of this. They also would throw weird bulb out warning lights on the dash for all the lights on one side every now and then. Same fix though. I am pretty sure that the water inside the tail light housing would corrode the contacts and throw the bulb out warnings.
By the way, it sucks to get the old taillight housings off because you need a small plastic trim tool to wedge between the outside edge and the rear quarter panel since the plastic pop pins are usually in there tight and you don’t want to use something metal due to the risk of damaging the paint.
I did this with my A6 and it worked like a charm. The lights from the factory seem to have not been sealed too well. Once I fixed mine I never had an issue again
If it was me having this problem, then I would look on Google for a write up or YouTube video regarding “clear corner mod” or “hid retrofit”. Lemme explain…
The clear corner mod is when you remove the amber part of your headlight housing, to clean up the look of the headlight.
A proper HID retrofit involves replacing the lens in the headlight (basically to avoid being the douche bag with headlights aimed too high).
What both of these things have in common is the removal of the bezel/front of the headlight housing from the back part of the headlight housing where the light bulb plugs in. It involves heat to soften the adhesive. I haven’t done this process myself, but over the years I’ve browsed write ups and YouTube videos, covering everything from heat gun technique, to putting your light housing in the oven at the right temp for the right amount of time. Once the adhesive around the perimeter of your tail light housing is warm and softened, then in your particular situation, you can re-seat the adhesive along the entire perimeter, and hopefully rectify the problem.
Otherwise maybe check the bulbs for gaskets/grommet (?) where they twist into the tail light housing.
YES!
SO HAPPY to finally log in here and see replies to my (admittedly trivial!) query! Was just looking @ my condensed lens yet again today accompanied by resplendent sighing at the craptastic appearance. Sigh.
I also noted I should have better quantified my issue - it is precisely as pictured above, just on the other side… moisture solely confined to the clear reverse portion of the lens.
Regardless, I’m relieved to hear this is such a (lameass!) problem plauging C6’s in general and not isolated to some “issue” my particular car seems to have experienced under prior ownership… which… would have also just haunted me wondering WTF the fukker’s leaking. SUPERCOOL!
Should I use a trim removal tool to pry it out? Any uberninjotic brastrap secrethandshakes in this regard are - as alwayz - mucho appreciatto! 
thanks all!!!
In the following video, you can clearly see how to remove the tail light from your particular car:
“How to replace rear light bulb on Audi A6 (C6 4F)”
Please “like” the video if you watch it. At 2:15 in the video, you can see the seal/grommet that sits between the pale piece of the tail light housing, and the red piece of the tail light housing.
For a fix that is probably going to be permanent, I’d suggest that you go to Home Depot and buy some “rubber mastic tape 2228”. This is NOT “rubber tape”.
Mastic tape is best imagined as a product somewhere between electric tape and Silly Putty. It can be trimmed into a new seal/grommet to replace your existing leaky seal, and the overlapping areas of mastic will basically melt themselves together with the pressure of putting the light back together.
Obviously take your tail light off and dry it before you put mastic on. I’d also suggest changing ALL of the bulbs in that tail light while it’s apart. Any time that tail light gets taken apart in the future, then you’ll have to re-do the mastic. All new bulbs for that tail light will certainly run you less than $10, even at the dealer.
Given that UK dealers will quite happily resolve this matter FOC (IMHE) is there a difference in how you guys across the pond get dealt with or is it just that you guys like doing this stuff yourselves?
AoA doesn’t really take care of us once we are out of warranty. So that’s why you find so many diy’s from us over here.
This.
So a couple of days ago, this video was one of my “suggested videos” by YouTube, and what a great coincidence:
A bead of silicone around perimeter of light (where back snaps into front) might be easier and faster than trimming mastic tape. There’s also a good demo of determining where the leak is coming from.
Also, there’s a method shown to dry out the inside of the light housing (with heat gun on LOW setting or you’ll start a fire). Side note, heat guns are cheap.
And if there is a rubber grommet/washer missing where your bulb goes into the housing, then I’d suggest a tight wrap of mastic around where reverse bulb plugs into housing, AFTER re-installing reverse bulb. If the reverse light is the common problem with these cars, then maybe the stock rubber washer is inadequate where the reverse bulb twists in.