Man, that like a pretty good repair, nearly like plastic welded. If the material you used to repair is any good, it should hold. Looks like a poor design, a "V" with a forearm is only going to want to spread the bottom.
If a replacement cuff is mega-costly, order a piece of Kydex 9at least .125") to make a "liner" for the cuff. Heat/soften it in the oven, form it inside the cuff, let cool, trim, and use a good plastic epoxy to bond them together.
You could always cut the other side off, get a piece of 6" PVC, half it, contour however you like, and epoxy it to the "base" piece. You'd never break the radius of the pipe, and would allow you more room.