Hmmm not sure slot will cool the pad. Even slots on the disc will not give more heat dissipate quicker. The slot I was told by brake people is they sweep the excess dust from the caliper and make the braking better. ... :dunno:
I don't think it is a pressure problem and I doubt the braking force is that much... not that can crack metal on its own anyway. I think heat is more of a factor here prof.
I also think the stock wheel may not give a lot of cooling to it. I really dunno. I only found in my car when going from stock rim to a wider wheel base sports rim I have lower track temp... but I have AP racing caliper at the same time.... so dunno again.
But my theory on what happens to WAY is overheat over a period of time, crack after metal fatigue.