It's a magnetic cam timing adjuster as tkamiya said. The knock sensors are on the block.

The EPC doesn't show a seal between the magnetic adjuster and the head front cover. From the looks of things in your photo, and mind you I don't know squat about the M119, it looks like the leak is between the front cover and the head rather than between the magnetic adjuster and the front cover.

Seems to me that there should be an o-ring between the magnetic adjuster and the front cover.

Sixto
95 S420
87 300SDL