[TramPower4000]

Hi SD1too. Well, it appears you were almost certainly correct. Eventually, after oil was contaminating the coolant more and more, the repair shops (X2) emphatically advised that the head gasket was damaged, even though I suggested a number of times that the oil-water heat exchanger (which they called the 'oil cooler') may be the culprit. Both shops denied this. So the original shop replaced the head gaskets, saying both were damaged (who really knows).

Oil then reappeared in the water. To make a long story short, it transpired that the oil cooler was indeed damaged, and leaking oil into the coolant. Indeed, oil started leaking onto the road from the oil cooler! After replacement of the oil cooler (by a different shop) I was advised that the oil would continue to appear in the coolant for a while due to oil contamination in the cabin heater circuit, which apparently is a monster to remove and wash out.

Anyway, I'll see what happens. The engine is running well after its second head gasket job!! And the oil contamination seems decreasing. Thanks again for your advice and suggestions ...