I have a 2001 Bonneville and its CAT went bad. I bought a exact fit OEM replacement for around $200. Decided to have a discount muffler shop install it. When they put it on the lift, stated it would be to hard to install bolt on style due to rust.They offered to install a aftermarket CAT, parts and labor for $100. I went with the aftermarket. It worked well, passed emissions the next day.
Lesson learned, for the CAT for our vehicles, the aftermarket replacement was much less expensive than the OEM style, may install easier and works flawlessly.
2001 Bonneville SSEi, 219,000 miles.
Whats in my driveway:
1998 Chevy S10 4x4 ZR2, 1999 Olds Bravada, 2001 Pontiac Bonneville SSEi, 2007 Ford F-350 regular cab 2WD, 2008 BMW 335i coupe (Wife'* replacement for her Bonneville). The Bonneville is my favorite of all the cars in the driveway.