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.