My 88 Bronco, 302, 83k miles has the air tube just prior to the cat rotted off. The local garage (not Ford) replaced it with a silicon hose and said it's good to go. Lasted a week and burnt through! Been replaced again by me to get it through inspection but again only lasted a week or so. What's the deal? Am I looking at a catalytic convertor that's clogged and overheating?.. If so, what's it going to cost me?