While our team was conducting the replacement of the heat exchanger & oil filter housing, we noticed a mild corrosion on the cylinder head as well as oil filter housing. Over time, the existing coolant deteriorate which heats up when the engine is running and caused this corrosion. This shows how important it is to regularly renew your coolant. Changing to a new complete oil filter housing (not just gasket) is necessary as the coolant flow line is warped and coolant may mix with engine oil, which will then cause further issues.