What is the diameter of the bolt at the failure point? It's hard to gauge the size in the photos.
The taper fit should keep the bolt from wallowing in the arm, but any load support provided by the shoulder would be lost if the taper locked in first. If the shoulder makes full contact before the taper locks in, the benefits of the taper are lost. In other words, a proper fit would require absolute precision on both the bolt and the steering arm, something that seems almost impossible in a production situation. Once it is assembled, visual inspection isn't very useful, because the failure point will be hidden from view.
I'm not a metallurgist, but my limited experience with stainless hardware has been that the threads tend to gall and seize when torque is applied, and this causes the bolt to fail when disassembly is attempted.
Bill in FtL
