Here is a recent thread I started on the topic;
http://www.keystoneforums.com/forums...ad.php?t=40045
I have repaired them multiple times by just cutting them off, redrilling the holes and reattaching the ends. Each time they break again over time. In past research I believe I recall it being said that the flex guard had some sort of material inside it to keep it from breaking. I figured there was a wire or something in the thick little band at the time....there isn't. It's just a piece of flexible plastic sandwiched between two pieces of metal under the body that flexes every time the slide goes in or out. Of course the other end swivels on the rod that the other end of the flex guard slides over.
When I cut the flex off in the past I would extend/retract the slide to make sure it wasn't too long/short and it wasn't, BUT, that plastic belt sure bends back and forth no matter what which undoubtedly leads to failure at some point.
This last time I decided I wasn't going to try to use the same method and did some research on ways to stop the flex. That solution was a hinge as mentioned in the post above. Haven't got to use it yet but watching it work gives me very high hopes that the issue is now solved.....I hope. We'll see in a few months. I looked for a piano hinge but instead had to use something like this;
https://www.homedepot.com/p/Everbilt...3594/203170039
Believe it was 2 1/2". Nothing would match the pre drilled holes in the flex guard so got something where I could drill new holes. Time will tell and good luck.