It is a die crack. This area has seen many die cracks though the different designs. The metal formed to make the bust design, makes the die try to flex. Not something a tempered die wants to continue doing as the die ages. Reminds me of a Peanuts cartoon I remembered by a few decades ago:

I remembered it, and rechecked and it was in the mid 1950's when it first came out. Somethings are broken when they start to be flexed.

I remembered it, and rechecked and it was in the mid 1950's when it first came out. Somethings are broken when they start to be flexed.























