1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 254Get this manual
GEAR HOUSING
7Place gear housing in FORWARD gearGear housing will ratchet when propeller shaft is turned clockwise8Apply 6.4mm (14 in diameter bead of RTV Sealer on water pump base
aRTV Sealer 9Install gear housing as follows: aPosition gear housing so that drive shaft and shift shaft extend into drive shaft housingbMove gear housing toward drive shaft housing while keeping mating surfaces parallelcGuide shift shaft through hole in mid-sectiondGuide water tube into water tube guideeRotate propeller counterclockwise while pushing upward on gear housing to align drive shaft splines with crankshaft splinesfGuide end of shift shaft into shift coupling yoke under cowl