Marine stern drive with lubricated and sealed output coupler

A marine stern drive (10) has an engine output coupler (60) driven to rotate about an axis and having a hub (70) with a splined axial opening (72) therein which is open-ended at the front and rear. A splined output driveshaft (78) is received in the splined axial opening (72) of the coupler hub (70) and is operatively coupled to the boat propeller (20) to drive same. The coupler hub (70) has a grease fitting (74) therein and a grease passage (76) extending from the grease fitting (74) and communicating with the splines (80, 82) to lubricate same. Front and rear sealing O-rings (84, 86) trap and retain the grease therebetween to maintain lubrication of the splines. The axial opening in the hub has a forward splined section (88) and a rearward nonsplined section (90). The driveshaft has a forward nonsplined section (90), a splined section (94) axially rearward of the forward section (92), and another nonsplined section (96) axially rearward of the splined section (94). The driveshaft is received in the hub opening with the splined section of the driveshaft and the splined section of the hub opening partially overlapping. The forward nonsplined section (92) of the driveshaft is received in a portion of the splined section (88) of the hub opening forward of the overlapping splined sections. The splined section (94) of the driveshaft rearward of the overlapping splined sections is received in the nonsplined section (90) of the hub opening. The nonsplined section (96) of the driveshaft rearward of the splined section (94) of the driveshaft is also received in the nonsplined section (92) of the hub opening.