Rear Finish Mower Question about a Mower input gearbox seal

[GreenMtns]

The input seal started to leak on my King Kutter 5 foot rear discharge mower. I am going to replace the seal and am in the middle of disassembly. According to the manual that came with the mower the seal is held in by a snap ring. There is no snap ring on this shaft and no groove to place one in. My concern is that just pressing the new seal in will result in the same problem.
Has anyone else run across this problem and if so what did you do?

Thanks