He helped me troubleshoot a burning smell. The car has a very slight leak from the driver's side rear of the valve cover gasket, which happens to be directly above the hot exhaust and turbo. Since the leak is very slight, he recommended just keeping an eye on it.

I just had a pressure/smoke test done at Autobahn, and they fixed a couple of leaks. However, I'm still not getting full boost, so I had Jamie check the fit and clamp tightness of all the pressure tubing. Everything was in excellent shape. (Thanks Autobahn.) After doing some pulls on the highway (and avoiding speeding tickets) he thinks it might be a control issue (solenoid) instead of a piping leak. Believe it or not, he actually recommended that I take the car to Autobahn, citing their experience with Audis. That alone speaks volumes about the integrity of this shop.

I just went onto the B5 S4 archives and found that the N75 valve could indeed be the culprit.

1.8T's and you've got 2 of them. I also noticed that they were the stock part...

That's why I never suspected any of these. That was just 3.5K miles ago!