Yessir. Mine had 135k when I couldn't clear p0420 as well. Finally bit the bullet and order a new CAT from RockAuto. Fixed the problem. Posted the video to help others in the same pickle.
@MattLahmeyer did you have to remove any other components to take out the cat, was anything in the way that needed to come out? Or is it just loosen it up and pry it out type thing.
I think you are referring to the fastener that has a Phillips head but just spins when you try to unscrew it. There is a central piece surrounded by a washer portion. You have to gently try to unscrew the central part and then as it backs out grab the center part with some pliers and pull gently to release the whole unit. Or sometimes just have to use a razor blade to pry the central part out and remove with pliers. Once you get one out you can see how they are constructed and it becomes easier. Good luck.
I am not a mechanic but am pretty handy. I had a helper that is a much better "mechanic" than me and together it took about 3 hours start to finish. I made sure to spray all the bolts that would be loosened with penetrating oil every day for about 3 days before we began work. As you know one rusted bolt can take a lot of time. Luckily by pretreating with penetrating oil we didn't encounter any difficult bolts.
