I dont think the om601 has an oil cooler of either sort. There is a transmission cooling circuit in the radiator, but in my experience that results in pink transmission fluid.

There was a recent change to synthetic oil from dino. The residue in the coolant tank is very black and oily, but not milky brown.

What does the test kit look for?

edit: Saw the kit on UTube. Its a sniffer for exhaust. Im guessing I could have an oil seep to a coolant galley and not show exhaust gasses at this early stage. I would really like to know exactly what that residue in the tank is-- thats the test I want.