I took the car out today to sell. When the buyer started checking it over, apart from a droopy rear spring, he identified a much more serious problem. The expansion tank, rather than being opaque plastic was black and lifting the cap off, it was covered inside with a foul-smelling orange 'mayonnaise'. Initial thought was a head gasket on the way out and that has the potential to be ruinously expensive. The buyer suggested that a head gasket going on 2.5 TDI (180) engines is rare and it might be a busted "water cooled EGR valve". Still expensive but not so much as it would be beyond economical repair. What are your collective thoughts on this? What sort of money am I talking if it's worst case and a new head gasket is needed? Does it reall yneed the whole engine coming out? A bit of background - car is a 2002 model, has done 106k and has FSH. When the car was last serviced, the EGR gasket was replaced - apparently it had been driving aroudn for a while w/out one. At 103K, it had new 'stat and water pump so I assume the coolant had been drained out then and no-one mentioned any problems. Either becuase there was no prolem or they kept it quiet. Thanks veyry much in advance.