Anyway, I upgraded from the GQ to a GUIV 3.0. After reading the wisdom I fitted an intercooler fan over the weekend. When I took the shroud off and had a good look the intercooler seems to have a hole in it. The greasy soot is in the front left hand corner.
The soot isn't too bad yet and obviously will get worse over time. Good news is the car is still under warranty. I'm going to explore an aftermarket cooler with the repairers and split the cost - dependant on the cost of an original nissan one.
The advice I seek is is there a quick fix (like sealant) if I can't get the repairs done or I end up in an argument with the dealer (been there before). I'm happy to install myself but would rather an aftermarket one. I also depart next week for a 4 week trip.