I see posts here and there talking about eventually all carded Joes o-rings will break,even the loose Joes o-rings will break I read. I have seen this firsthand one time and that was a misb Zartan which I bought off ebay and half of the o-ring was broken and dried up and was being stretched. The box was obviously left out in the sun too. This Zartan appeared to be very abused. I have never experienced this with any of my moc Joes or loose Joes.
My first Joe was a 1985 Crimson Guard. It's joints are the loosest I have ever seen in a Joe and it has alot of paint rub, but I NEVER abused it or pulled the top from the bottom trying to find out how far the o-ring would stretch. It's o-ring is fine to this day, as are all my loose Joes.
IMO, if Joes aren't 'stretched' or abused (left out in sunlight, thrown, shaken if moc, etc.) thier o-ring will NEVER break. I think a handful of people like to say the o-ring will break so they can make themselves feel better about not owning expensive moc figures.
Conclusion.....urban legend (if not abused of course)