Under the bilge drain hole?
If so, check your drive oil reservoir level. Its either a tubular cylinder or squared container somewhere mounted on your engine or transom.
If its really HIGH then your oil heated up while the drive has been sitting in the sun, and it bubbled out of your reservoir. Not a big deal, just check the level and go boating.
If its really LOW then check your transom under/behind your motor; under where the coupler goes to the transom assembly. If you have traces of oil dripping down here, or anywhere else in your bilge, you have a drive oil leak between the reservoir and the drive, and this is not good. It sounds like the drive oil leak may be inside the bellows which is the worst place for a leak, and you don't want to take the boat out as there could be other complications.