I notice what looks like incomplete brazing at the seat cluster lug.
My old (60s Holdsworth) frame snapped by a cable-stop on the top-tube. I lashed it together with a handy piece of discarded rope and a toe-strap, and rode the 12 miles home. Its replacement was already on order.
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Pretty prescient to have ordered a new toe strap! it's annoying as hell to ride with just one.