Karnak

If hitting a curb did that, i really suspect your rim/Wheel may have issues too cause usualy from my experience (yes I hid a few curbs in my life) the Wheel, bishings or balljoints etc take the beating. For something like this to be broken, if nothing else is damaged, then I would seriously consider this a defect in manufacture. There is no way imo that a part that big can crack like that without having other additional dmg somewhere on the rim/Wheel, tab bushings, balljoints etc,etc. at least I have never seen it myself. But like others said, its always a game between the dealer and Customer when it comes to warranty issue, so at that point its your call, but I would probably try it.