I have a VW camper fliptop with the TDI conversion engine in.
I did a 450mile trip last weekend and it run sweet until I got 10mile from home and the water temp gauge started to climb. I put the heating on full blast and sure enough the gauage started to go down. But with about 5 mile to go it shot up to red flashing light danger zone. So I pulled over and to my amazement the radiator overflow tank was overflowing and spitting out some nice sludge which combined "oil & water" I then looked in the radiator to find the same sludge in there. So after seeing this I checked under the rocker cover cap and it was clear. But from experience it is pointing towards a head gasket fault

Just to clarify it still pulls fine and is not throwing any blue smoke out.
So members I need some help here. Do you believe like me it is the head gasket that just needs replacing. If so not too bad or do you think it is pointing to something else? Also how do I get all that sludge out of my water system? Do I just use a flushing solution?
All help would be appreciated.