My theory is that cracks initiated quite quickly in the original chassis (ie micro cracks that are not visible) - without the bolt in brace, they also propagated quite quickly and became visible (we shared this experience with many early owners and had a rebuild). The bolt-in brace has at least slowed propagation for those with the early chassis but with the number of cars with the brace now showing cracks, it looks like not being enough. The good news so far is that the replacement chassis with welded in brace (and other changes?) appears not to crack...
