Don't know the particulars but I have a friend who's Dad had the same problem many years ago with a 4020 PS It went too long and they had to remove a housing (?) rear end (?) and have it machined and bushing installed because of the wear.

Like I said don't know all the particulars of what exactly happened just heard him tell many times about it how it all started when the PTO would not stop turning.

Needs checked out before it gets too bad.