You might have coolant inside the transmission, production before 09/03, on w203, w209, w211 radiators were made by Valeo. coolant will leak thru the trans cooler lines. Depends on how much coolant, they are different steps to follow to repair the problem. Step 1: check if there is an update transmission control available. with the update transmission control module and the problem still persists. perform glycol test. Worst scenario , replace torque convertor, radiator, flush the trans. sometimes you can get by just replace the radiator and flush the trans, but like I said depends on how much coolant in the trans, hope this will help.