Thanks for all the comments.
Reason the box tube broke......... there are torsion bars under the applicator, and are hooked to brackets just behind the break. Those bars create tremendous downward force, pulling on the box tube. Unit broke the box tube for previous owner, but previous owner fixed the break by merely welding the break.....no fishplate. That break was not noticeable due to a good job of painting and grinding, until it broke the second time, which exposed the weld inside the box tube.
We fixed it by fishplating on the sides, since brackets were in the way top and bottom.
We will see how it handles.........but at least now there is a lot of metal ahead of the torsion bars.
Again, thanks.