Joep, your a-arm is the second cracked one I've seen in 40+ years of messing around with the car, which includes wrecks. So I suspect its not a common defect. And that one was also a lower rear, which is the most highly loaded of the a-arms on a Pantera. So if I was especially worried about a-arm cracking, my attention would be upon lower rear a-arms. Finally, their saving grace is while being quite light, Pantera a-arms are mild steel that easily gas or arc welds. So maybe some owners that find this problem simply fix them.