td6 head trouble

morning folks ,
while out checking a few bits on RR I noticed there was quiet an amount of black oil in the expansion tank.
oil level has dropped no signs of water in the oil or on oil cap,
is there anywhere else oil could get into the cooling system a part from head gasket failure on the m57?
roughly how many hours are in doing the head, rough cost?

First I know nowt about the TD6 engine, but having had that problem on another engine, I suspect a failure in the oil cooler if it has one. If it has an oil cooler and connected to the engine coolant system, the internal seals can fail. The oil being at higher pressure than the coolant migrates into the cooling system and ends up in the expansion tank. So first step is to find the oil cooler ------

I never thought of that, will look now