The various suggestions to identify the leak are, of course, germane. This does sound to me, though, like the upper shaft seal is leaking - it drips down in a subtle way and it's hard to figure out where the oil is coming from.
It's an easy fix - just detach the drive shaft coupling, scoot the engine back a bit, remove some retaining bits off the shaft (big hand sledges and chisels-as-wedges may help), then pull the old shaft seal and replace - it's a 60-90-10 single lip rotary shaft seal - don't need a stainless steel garter, but do goosh it up with grease.
Then again, we're all just guessing at the source of the leak :-)
Good luck with it - let us know what you find.
Beers, Craig SN 68 Sangaris Tropic Isle Harbor, FL