And I agree, first port of call should always be get the car scanned. There is a lot to gained from reading fault codes or logging sensor data.
I never said it was explicitly a head gasket failure, but from there description it does sound like one. You implied that because you have never experienced it throughout the 35 variants of 1.8T that you have owned, that it simply cannot happen. Just because you have experienced 'crazy temperatures' from the exhaust gasses and never experienced a head gasket failure because of it, has no bearing on whether or not it can happen to a modified or standard car.