After a bit more questioning the owner said they were used many years ago. Then they were sent to JBL when the service was still available for a complete re-cone. And since then never used. So, this does not sound so interesting after all. I guess I will just wait it out. Even if offered a proven new pair it still begs the question as to is it time or use that kills the surrounds. At this point I guess I will wait and address the problem if/when it occurs. So far so good. Not too worried about those magnets though, I'll tell you that!
Thanks