Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 249Get this manual
3 Slide the rubber sleeve at top end of shift shaft down so that it just touches the oil seal in the bushing
Drive Shaft and Pinion Gear
INSTALLATION
Note: If Ihe original shims were not retained or if pinion gear, drive shaft, drive shaft tapered roller bearing and cup, or gear housing were replacedstart off by installing 0.038 in (0.96 mm) shim(s) Note: If the original shims were retained (or measurement known) and none of the above listed parts were replaced, reinstall the same shims or same amount of shims1Place the shim (s) into the drive shaft housing bore
aShift ShaftRubber Sleeve
cOil Seal
dShift Shaft Bushing