If your current slider is still mostly intact, a
9.50"/240mm x
1.50"/38mm x
.125"/3mm steel strip JB Welded to the top of the lower slider section & drilled for the rear mtg screw should beef it up quite a bit. The raised ring around the screw hole would have to be cut off flush first, then the plastic & metal roughed up before gluing (at a slight angle towards the screw-hole area). After curing the screw hole can be drilled (shoulder-screw measurement TBD), then you should be good to go. Normally I wouldn't post this until after I'd modified mine & put several rides on it, but I figured why wait. This may work on some broken ones as well, provided there's still most of the lower slider left (the rear hole area won't be needed, but the curved part around the front of the pivot area will be). The .125"-thick stainless will fit real tight under the swingarm-pivot area, making it rock-solid against upward chain whip. It'll eventually wear through to the metal, but it shouldn't flex-crack and will put up a lot more fight.
316 stainless flat bar (use 'Create a Custom Size' button)
IMO the ideal solution would be to double the slider thickness around the front of the pivot, then increase the bottom run thickness a lot to fit against the swingarm bottom.