just a guess, but isnt that where the shift cable is supposed to go thru
check to the right of the ball gear, takes a flat blade screwdriver. http://www.sterndrive.info/id12.html
All the fill/drain plugs on the Stringer are on the starboard side of the drive. That screw you're pointing to is for a clip to hold the shift cable (which goes through the hole just to starboard & below that screw) in place.