I had a spotty connection on the upper radiator hose. It was leaking at the bottom of the clamp, hard to spot. But it was leaving a puddle every time I parked. I finally noticed a drip trail inside the radiator shroud.

What was happening is that it was only leaking under heat and pressure, when cold it would not leak.

Long story short check the simple stuff first.

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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