I've been doing some reading on what would cause the cat to fail. I've read things saying it should never fail, others saying it eventually wears out. The dealer says they eventually breakdown. Anyone know what the deal is? I ordered the new cat yesterday and will inspect the old one when I take it out to see if I can determine the cause from there. If there's something going on with my engine, I need to address it because I know that will kill the cats. But are they really supposed to "never" fail?

I've got just under 115,000 miles and a friend had to replace her cats around the same time (although due to MAJOR engine issues, misfires, oil leaking in cylinder 1, rich mixtures, etc.).