2006 E320 CDI, 133K miles. A few drops of oil on my garage floor prompted me to check oil level, 6.2 qts vs. 8 when full. Found what appears to be a seal of some sort that's obviously been leaking awhile now. See pics. It's a cover plate on a part integral to the injector train, i.e. head. The part number doesn't get me anywhere, and I can't find anything that looks like this on the diagrams except maybe the timing cover. Anybody know what this is?