Mercedes MBE 4000 oil leak

Hi all. So, we have a truck where I work that's developed a pretty bad oil leak. It's an '04 Sterling with the Mercedes engine. I crawled under it the other day to try to pinpoint the leak. Sprayed brake cleaner all over the suspicious area and ran the truck for a few minutes. Near as I can tell for now, until I do some more cleaning, it's leaking from under the left rear engine mount bracket. I found the bolts to be loose. I tightened them again and it doesn't seem to leak as fast now. I don't see any oil coming from the clutch housing. How and/or why would there be oil coming from behind that bracket? Or am I missing something else?

Engine could really use an overhaul, it drinks coolant, there is a trace of coolant in the oil, a fair amount of blowby, but they want to replace that truck this year, so I just need to limp it along. Has anyone had this particular issue with this engine? Thanks in advance.

 

Forgot to mention, it's got just over 300,000 miles.