Vac u Seal works for systems that are about to be put under a vacuum
AFTER YOU APPLY IT !!!!!
Since the tube is fine ; adding it now will only stop future leaks, which you don't obviously have after 56 years ! We ONLY use it at NASA when we assemble parts, then put them under a vacuum during leak testing to suck the glue into the leaking joint. Since it's not leaking adding it now,( and if your lucky finding the spot where it might leak in the future) is a waste of time.