[C320-list] Black Oil in Mixing Elbow

[Uckert, Kevin]

I noticed a black oily substance dripping from the mixing elbow. From under the elbow itself. It appears to be motor oil, but not sure.
This Yanmar 3GM30F with 180 hours, runs great, no missing, shaking etc. No loss of engine oil, just a mess as it is dripping onto the transmission
case and to the starboard side of engine compartment. Any idea what this could be? The yard mechanic is mystified too.

Thanks all.

Kevin