Originally Posted by
Darth Lefty
I was wondering about the pantographing. Stress left by a stamp could start up a crack that would collect moisture.
The pantographing likely isn't the issue. It's done during the manufacture of the cap, and very common. You can even see that the cap chose to break, not at the base of the "i" but neatly between it and the "a".
Failure of theses solid end caps isn't all that rare, and is the result of the entire assembly being too stiff, so all the strain of seat stay flex is taken up right at the end of the braze fill to the lug. It's analogous to tube failure right at a weld, and other failures at joints which become the fulcrums of flex members.