I haven't heard of one breaking, but they do sag.
I pulled the Posie's Super Slider from my 32 perhaps eight years ago.
Nothing was wrong with it and it was working ok.
Installed a Durant Mono-Leaf in an effort to gain some front end travel.
(I should have notched the frame - you can bet the 31's frame is notched.)
The travel was gained, but now that it's sagged it's about to where the Posie's was.
I did add a 3/8" shim - in addition to all of the shims that Durant supplied - much more and part of the shim pack would be out of the crossmember.
I saw last night on fb about John. The world sure lost a great one. I'm going to miss his humor, advice, and perspective from another portion of the world. Rest in Peace Johnboy.
John Norton aka johnboy