Don't know if this applies to yours or not...
On mine the pan was leaking. When I did the filter change I discovered that there were three short bolts and one long bolt, each with a set of "wings" to spread the pressure evenly. When I pulled the bolts, I notice the left rear bolt had the "wing" caddywompus across the corner lips instead of flush against the pan. The last person to change the filter didn't pay attention to where the bolts came from and obviously couldn't get one to tighten down so he improvised. On mine the long bolt goes at the right front corner.
Being bolted in incorrectly, plus the seal being pinched at that corner, was causing a small, but messy leak.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.