One thing that hasn't been mentioned when you 'pull' the ring back is to use both hands... (after lubing both the PTO shaft & the coupling with a lanolin lubricant) I cradle the coupling in the palm of my hands, then 'pinch' the ring back between thumb a fingers...
Once I've got it sliding onto the shaft, I can release the ring either before or after I've advanced it regarding the PTO groove. You can hear & feel it lock into the groove.
Then it's just a matter on getting/cleaning all of the grease that has jumped onto your clothing... and then everything that you've brushed up against... which should take a few days. :laughing: