Yeah, I was gonna say that, in my (admittedly limited) experience, the failure mode for cats seems to be getting blown out, not getting plugged.

I paid only $100 for a new MagnaFlow cat converter, after which my 420SEL passed California smog with flying colors. As a matter of fact, the emission numbers were just about zero!

But I had to cut a hole in the MagnaFlow cat and weld the bunghole for the O2 sensor from my old cat into it. Otherwise the MagnaFlow cat was just about identical to the factory-issue item.

All right, all right, let's not hear any jokes about Bungholio, OK? Every time I say the word "bunghole" around my shop, I never seem to hear the end of it!