Just noticed this yesterday. Small drip of oil on the driveway, coming out of the water intake. I've seen it could be a crankshaft seal or just old burnoff that has congregated in the exhaust. The motor hasn't run in a few weeks and has just been sitting straight down. Something to worry about? How about the grunge around where the gearbox and lower unit come together (pictured)?
(edit: motor is a 2-stroke)
(edit: motor is a 2-stroke)