cossie 4x4, greens, stage 2, 26psi. since changing oil from cas magnetec 2 mobil 1 15:50 started gettin oily gunk in the header tank, there is no sign of water in my oil at all, group a head gasket showin no leaks or stains also fitted is a swirl pot and a oil seperator can anybody shed any light on this.... cheers.