The injection pump is internally lubricated by engine oil. There are oil passages through the front end of the IP where it attaches to the engine.

There are cover plates on the IP, on the side, and the bottom. These have gaskets that get old and leak. They are relatively easy to change, with the IP installed, but you want to make sure that you don't get contaminants in the IP.

There is also an o-ring around the neck of the IP that can leak. This requires removal of the IP to change it, so you have to be prepared to reset the injection timing.

Clean the area really well with solvent in a spray can (we call it 'brake cleaner' here in the US) and you should be able to find where it's leaking from.

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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