i have had a few problems with "suction" or air trapped. and i was not physically strong enough to over come the sticky grease, and air trapped.
and like others said, was forced to tie implement off to a tree or truck. and then hook end of PTO shaft onto back of tractor draw bar. with a chain/rope/wire and pull PTO shaft apart. and tapping with a hammer.
there is no "special" thing like a snap ring or pin, or like, that keeps the PTO shaft from fully extending and coming apart into 2 pieces. reason why care needs to be taken when you "cut down" new PTO shafts, to have correct overlap.
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speaking of being fairly new. you may need to cut PTO shaft down. to properly fit the implement and your tractor.