Check the back left corner, the EGR valve has coolant lines going to it, that cool the EGR valve, as well as the EGR heat exchanger that is located under the intake manifolds.

Several small rubber hoses back there that could have sprung a small leak.

Once you get the leak sorted I recommend a water pump and thermostat change just for trouble prevention purposes.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech