You dont say what model!
but if if its black, smells burnt or of gasoline it is almost certainly just unburnt oil from the fuel, as nwcove suggests, coming from a leg drain hole.
It it was gear oil it would have the typical rotting cabbages smell of an EP gear oil
See the item on the Engine FAQs board entitled " Oil leaking around lower unit"
http://forums.iboats.com/forum/engin...nit-by-iwombat
Always say what engine you are talking about. Year, HP and whenever possible model number.
Evinrude made many different engines in 1964