Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL
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