Sam, just get under it with a bright flashlight and look for a spot where it's coming from. Take a first look for the obvious and if it ain't clear to ya, wipe it down with a rag and let it sit all day or overnight and then look. Sometimes the oil will blowback in the wind and hide it's source.
Like Ian said, sounds like the NS or a small crack in the filter. If it's the latter, it has significant pressure while running and it should tell on itself. Oil leaks are easy to find.
But den it may jus be sweat drippin' out from undah all dat hosspowah.
