that the throttle cut off valve to give a diesel a crispier cut off, what you are seeing is the oil coming out of the boosted side of the intake system, audi oil is very thin so over time it can get out of the seals around this valve, or you may be looking at a turbo letting excessive oil into the boost system, as it is at the moment i would not get too worried about it, as at about 50-100 k this tends to develop due to perishing seals etc. if it get any worse then replace the valve! you cant get repair kits for them!