28390 (Mercury part 35983) is installed onto the horizontal gear train in the upper gear case of the Mercruiser outdrive.
To access this part, the threaded drive shaft bearing retainer - 28350 must be removed along with the lock nut 28360. To remove
this part, a special tool called a bearing retainer wrench can be used for easy removal and installation. This tool is compatible
with all models, including MC-1, MR, R and Alpha 1 and Gen 2 models. When working on the horizontal section of the drive housing,
make sure to replace the o-ring (82380 - included in seal kit) installed behind the part along with the locknut (28360). Make
sure to inspect the two bearings behind the gear for any play and replace if necessary. The seal kit, locknut and tool can
be viewed below.