New-ish S6 4F5 Avant 2007 owner from Finland chiming in on this awesome topic. Sorry for the long post, but I want to be informative (and rant alot).
Got a high-mileage one, 337000km+ on the odo. People keep warning me about it being a huge timebomb! %(
Still, thinking the engine should have gone south, years ago, with it’s 40000km, yes, you read right, 40000km long-life service. Hopefully giving it the TLC it needs now, I intend to keep it running and improve on it if possible.
I have poor documentation of service after 225000km, and up to that, no atm oilswap and a 40000km LL service plan. WTF?? Original owner and Audi dealer?? WTF? But despite the fact, it seems to be okay. Apparently has MTM V-max done (top speed limiter removed). Otherwise quite stock. Engine and trans pulls like it should.
Anyhow, the guy who imported this thing, apparently ran a 13.550sec 1/4mile on this almost stock familywagon 
Quite quick, but, I am heavily contemplating on schrik high lift/long duration cams and head porting, in addition to swapping the smooth economic quiet humane intake for the straight non neutered RS6 one, while modifying the intake, to allow for more cold air and less heat soak. Exhaust will be either a custom 3 inch cat-back with 3 inch “sport” resonators and mufflers, or the same with magnaflow or rs6 rear silencers.
Apparently the previous owner had issues with the car, and after the dealer serviced the car to an amount of around 10k eur, he still dumped the car to the dealer… so I got a bargain, because they just needed to get rid of their un-sellable shop queen.
I had an issue with the intake, flaps were stuck open. Apparently they cleaned the intakes but one “E-clip” was missing on one of the actuator shafts, so it was dangling loose. The brakes were shot. As first aid I got front discs and caliper slide pins and bushes from Audi, 926eur. Pads would’ve been 408eur, got cheap aftermarket phaeton/s8 pads instead, for now, 69e. Will look for cost effective aftermarket solution in the summer when I replace rear discs and pads.
Biggest problem I’m having, is the front coolant return pipe is leaking. It has rusted next to the welded joint. Ordered new pipe and the 3 or 4 adjacent coolant hoses, for about 250e. Hoping the culprit has been rocks and saltwater, and the rear pipes/hoses are still ok. Otherwise it’s prolly engine out. At the same time was going to replace thermostat and waterpump propeller. But the assembled oem pump/thermostat package cost 404e so I ordered the whole shebang.
I hope the maintenance will slowly go back to “normal” level on mine, and I can concentrate on enjoying this masterpiece of car I’ve got my nails on :devil:
Edit: more ‘old-car’/‘poor mfg’ problems
Forgot to mention my adaptive cruise control is working-not working-working and one front parking sensor is broken, one rear sensor wire has oxidized and broken off the connector… The ACC seems to have some sort of wiring issue, related to the leaking/spraying coolant overflow pipe and very sharp edges of the front bumper crash member (wiring is chafing on it and the coolant shorts everything).
Cheers!
Kristjan
