No, I don't know what is causing it. First break came at about 73K miles, second bracket break came at 81K, and this one came at 164K. They have all broken in the same place, too. They break across the opening in the bracket through which the pulley shaft from the PS pump protrudes.

And, yes, I have changed the PS pump, at 81Kmiles ('cuz that's what the Ford dealer said was causing the aluminum to fatigue and crack), and again at 145K miles, when the pump began leaking past the seals.