A friend of mine found a bit of engine oil in his diesel filter when he was changing it couple of days ago. He has a 1.9 BKC engine code. Not so long before that he got his car back from the dealer because of his car having too much pressure causing loss of coolant via the overflow and getting no heat at all in his cabin. Dealer diagnosed it as headgasket and now its sorted. Would the oil be there because of that or its a new problem?