I have recently aquired a 2.2 I-DTEC 8th gen (2010) estate. It has mayonnaise in the coolant header tank but none in the main engine. It runs fine, no loss of power or excess black smoke. Have been told its either down to the square shaped aluminium oil cooler on the oil filter housing that needs replacing or new seals or simply due to lack of use by previous owner who never drove it anywhere than to the local shop and back once or twice a day so it's got clogged? Any ideas/advice ?