If you have a PTO good chance you have a dual clutch. Take the inspection plate off, and look for rivets or part of the clutch disk.
You should be able to see the condition throughout bearing, it possible those arms that engage the clutch are broken, loose pins or adjustment bolts are worn.
Sounds like you will need to split the tractor to get to the bottom of things.
Bundy Bears has a great video on Fitting and Adjusting the Clutch Assembly https://www.youtube.com/watch?v=AZoe6RGbDl0