I have not seen this on here, and thought it may be of interest. A friend of mine has a 60 Corvette, with a stock 283 Fuel Injected engine. He has run it for years without any problems, driving cross country and all. Last year we had a run down here, and on his way home to LA( it was a triple digit weekend heat wise ), it overheated, and after cooling down would still quickly overheat. After going through all the normal business trying to fix it, nothing seemed to work. One day he had it up on his rack, and looking around, he thought, those mufflers have been on there for over 15 years, I think I'll replace them. Bingo, heating problem fixed, run's better, etc. The car doesn't burn oil or run rich, so it seems odd that they started plugging up. Its a true dual ehxaust, and they both were still pumping fumes alright.
I suppose if I have a question, since it would happen slowly over time, is there any way to check or inspect for clogging before they get totally plugged?