64 Valiant Radiator leaking at top

Had the same to mine. I believe it was caused by over 300,000 miles of rushing flow from the top hose. It actually worn thin the metal of the tank's top, I was lucky to find a local shop that had a new top.
But before that replacement, I [twice] made a 'patch' using J. B. Weld and fiberglass. Both lasted about two years each, on my '64 Dart daily driver.