They CAN be made to fly again, but not by spraying them with “Crack Bane”. It’s time to leave denial and wishful thinking behind, and start to face facts: There is nothing mysterious about the fatigue life of a metal aircraft structure; you can look it up in FAA Advisory Circular AC 23-13A. Every stress cycle takes a little bit out of the life of the structure. It does for glass, too, but not in quite the same way as for metal.