Broken Slide Stop Clip

The picture helps. I'm guessing that the likely culprit is the slenderness of the legs.

I'd probably try to put some sort of bracing across the "rear" three legs, and see if that helps. You might also try some diagonal bracing, as a little give in any of the bolted holes will allow some pretty significant movement at the feet.

I'm going to assume that you've verified that you have the feet all in a constant plane-- if you push down on each of the five corners, it doesn't tip slightly, suggesting that one of the other leg's a little too long.

I'm guessing these shattered because of shock or perhaps from being fully extended more than normal since the front wheel takes a lot of the weight when drawer is fully extended. The rail is acting as a lever where 10kg in the front of the drawer could easily be the equivalent of 100kg on that wheel when the drawer is fully open. The other thoughts are if someone where to lean on the drawer or if the cabinet was being moved and dropped.

I've seen replacement wheels, but they tend to be for specific rails/sliders, and I doubt you'd get a good result without a perfect match. For replacing the entire slider, I'd look for a replacement with a high weight limit. I've seen sliders in the US that are designed for 50kg, which I'm guessing would more than handle your load.