MY 1992 Camaro Z-28 limited addition just about went back as a lemon. It would just shut down...dead. Had it towed 3 different times and GM gave up. I wasn't successful getting them to buy it back, so it set in the garage after each warranty repair for 3 yrs on and off. I sold it to a collector w/ 5k miles after owning it for 6 yrs. Just before the buyer was flying out, I had discussed getting the exhaust repaired. I had a dual exhaust part # for what are State Police cars were running. A true dual exhaust. When we started to replace the exhaust we found the catalytic convertors were so bad, they were all but clogged. GM replaced them under warranty and the car never showed signs of dying again. They were the problem all along. Just about didn't sell the car after that. The Texan that bought the car was amused as I put a 1000 miles on the car in a week before he flew out. So, you would think GM would have discovered the problem, but no codes were ever thrown and the car was all new. GM replaced everything electronic on that motor 3 times...lol. So, you never know. I had at least 3 different very good mechanics looks at the car as well. We just didn't think about a new exhaust being bad.
If it hadn't been for it setting in the garage and not being driven rusting up the exhaust, we might not have discovered it then...