I've posted this elsewhere, but I added Pat's and in one situation, the shaft came apart. I was tilling with the 3PH in the down position when the rear tires rode over a mound. When the tiller went down, the PTO shaft came apart.
I continued to use it to finish that job, but I left the 3PH in neutral rather than full down in case it happened again.
I took the PTO apart. Mine had a roll pin driven through a hole in the yoke and tube. After removing that, I could use a punch / hammer to hammer the tube out.
A drive line supply place had the metric tube size I needed and sold me a drop piece for <$20. When I took the tube to the place, I found out they would press it in for just a little more, so I could have had the whole thing fixed and not gotten my hands dirty for <$50.
To fix it 100% correctly, I should have also lengthened the female shaft and bought new plastic shields. I figure that the shields might catch and break as they are not quite long enough now to overlap, but so far they are holding up.
Hope this helps.
Ron