I need some advice on a muffler for my 2nd Gen RX-7. I run a single pipe system, with two Borla stainless steel mufflers. The first muffler is approximately 12 in. behind the header flange and the second is at the back of the car. The front Borla lasted for four seasons before it cracked and split apart at the rear. I replaced it over the winter with a Borla XR-1 Sportsman muffler. That lasted less than 2 hours before it split around the perimeter about mid-way back. There is no point putting another Borla on. As such, I need some advice on what to use. I need something round or oval, no more than 4-1/2 to 5 in. in diameter or high, respectively, and 16 in. long. Any suggestions?

Thanks in advance for the advice.