Check your tranny fluid.
My SLK230 tranny is currently having a rebuild AUD$1500 due to a leaking radiator.
They use an integrated rad/tranny cooler unit.

If your tranny fluid is increasing = water. Milkiness in the tranny fluid is also a sign.

My mech is installing an external tranny cooler....much safer.

Next would be obviously engine oil for milkiness = head gasket issue.

 

check hoses, if you still have the belly pan on, you will see fluid build up under there. If not, then Billy22Bob suggestions would be next to look at. Good luck. But the intakes are too clean, as no build up of sludge from leaks. Doesn't mean it just didn't started though. May have not had time to show the build up. Good luck with your search.