[Tx Jim]

Welcome to TF
I don't remember ever witnessing a slip clutch removed when I was employed for 21 yrs by JD dealer. My guess is you need to replace ball(item 9) that was secured by grease fitting. Ball fitting in recess on gearbox input shaft should hold clutch on the shaft. Is your cutters SC grease fitting present or AWOL?

https://partscatalog.deere.com/jdrc/sidebyside/equipment/73653/referrer/navigation/pgId/112338

 

[Tx Jim]

As I stated previously I'm guessing ball is used as the SC to shaft retainer. I suggest to remove grease fitting & then slide SC on gearbox input shaft to see if a depression in GB shaft aligns with grease fitting orifice.