not sure if i answered you or not.. but if I didd, then I told you to check for thrust paly at the pto shaft stub, machine off. if there is any perceptible in / out play, the shaft will walk itself out of engagement.. chewing up the sahft end and collar inthe process, and in many cases mushrooming the end of the shaft too!
sometimes it's a detent.. not usually.
sometimes it's a damaged shift fork not getting you into engagement.. not usually.
the usual causes, as someone mentioned, are slipepd out split rings inthe bearing carrier.. damaged bearing carrier not holding the rings.. or bad bearing.
if you pull her down.. and nothing is broke.. consider repalcingthe seal if it leaks or weeps.... clean the gasket area up and install a new one, even if you have to cut it yourself. thin paperbaord works.. do not make a thick one.
park nose down and you won't have to drain oil..