I had to replace the original equipment catalytic converter after 234K miles of service because the flanges were rusting away. I bought and installed a Bosal cat from FCPGroton.com (great service!), but at 239K a leak in the exhaust system occurred from the cat. When the cat was removed, it turned out that most of the innards had melted and disintegrated.

So I order another Bosal cat from FCPGroton (for free, once I returned the old cat to them) and install it. About 100 miles later, I hear rattling in the exhaust system which turned out to be emanating from the cat. About 300 miles after that, I removed the cat and find its innards were well on their way to total disintegration.

What gives? The car starts and runs fine, with no bucking, hesitation, or apparent misfire. Spark plugs and wires were recently replaced; the oxygen sensor was replaced about 40K miles ago.