Hi guys, got a slight problem with my 2008 Audi A4 Avant 1.9 TDi. I've noticed it to be damp/wet directly under the expansion tank cap and dripping down to the bottom of the engine. I've lost the difference between the max and min mark in just over three months. I've heard there is a drain somewhere on the underside of the tank and releases if there is too much pressure. Could this just be that I need to get a new cap?? Or the tank needs replacing?? The car drives fine, no change in performance at all and the coolant is the nice pink colour and is very clean (had it change in a service 4 months ago) and I can't think it could be the head gasket that's gone otherwise I'd gave oil in the coolant or vice versa but I have neither....I think Any ideas would be greatly appreciated.