Interesting regarding the issue causing your Fire? As I have been working on some electrical rewiring, I noticed a rather large rip/tear in one of the Turbo charger Boots....replacing it now(53.00 for a piece of rubber, but it is what it is). Is that the part of your exhaust/turbo your referring to? I guess if it is I just dodged a big bullet. Either way, it should be less loud and hopefully improve fuel usage.
Amazing what you find when looking under and over the engine...mine is a CAT too, 3176b. Good Luck with the new coach.