1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 330Get this manual
BIG FOOT
Filling Gear Housing with Lubricant
1Place outboard in vertical operating position2Remove vent plug from vent hole3Place lubricant tube into the fill hole and add lubricant until it appears at the vent hole
a-Vent Hole b-Lubricant Tube 4Install the vent plug and sealing washer before removing the lubricant tube5Remove lubricant tube and reinstall cleaned filldrain plug and sealing washer