My 04 325i has overheated in the past but has been fine after replacing bad expansion tank. I recently discovered oil in my coolant. Not overheating, drives normal, compression @125 on every cyl hot or cold. Just replaced trans cooler to rule that out and I'm not sure if that helped? I've heard the oil filter housing gasket could be the problem but wasn't sure if it has a coolant jacket? Any input would be appreciated!!