I think the idea is that if you get a leak it won't just immediately fail and dump all of the oil. AFIK, all of the rebuilt and aftermarket ones use grease and not oil.

For most of the ones I have seen, the cracking appears to get worse and worse for a while. However, that could all go out the window on a long road-trip. I've heard some people are able to drive on them with some noise at slower speeds after they have failed. I personally wouldn't risk it...

Mine are in pretty good shape but I'm planning to reboot towards the end of next year just in case. I figure if I don't need it now, I will in a few years or more...

Dkr.