Specifically when?
I've owned 3 1st gen W bodies, and I've never seen an aluminum dog bone on any of them. And fwiw, if you have a dogbone that just breaks, then I would figure something else in the drivetrain could be amiss, depending on if it were cracked for a long period of time. You'd have to have severe fatigue or a bad vibration somewhere to put that much stress on the mounts.