Allis chalmers 5020

[Kelly underhill]

While bush hogging the pto suddenly stopped spinning. I checked for obstructions. The shaft still freely spins. 

[Tarheel]

 Back around 96ish, One of those was brought to me with the same issue. And it happened while bush hogging. The PTO shaft sheered right at the drive gear.

Had to split the tractor at the bell housing and then remove every shaft and gear in both the transmission and rear end. Axles and all. The very last piece to come out was the shaft. The job took a full work week for me.

That isn't to say this is your trouble, But I wouldn't bet against it.