If you're getting the oil level warning light, and the crankcase is properly filled I'd say the oil level sensor is heading south (if not already there). The sensor is located inside the block, and requires at least the pan be removed to access (if I remember correctly from my reading).
To find your small leak, clean the engine and bay completely, then look for the source of the leak. Very hard to determine the source when everything is oily.
'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.