In my experience, when part of a muffler system is rusted out, the rest is not far behind. It's probably best to replace it all from the cat back. I just bought an '84 240 which has a Midas system on it which is only a few years old. The tailpipe is rusted out already. Even if they guarantee the mufflers, you can still pay quite a bit for the repairs to the connecting pipes. The Midas system is also noisy inside the car. Several years ago I bought an '83 240 and put on a complete Volvo exhaust system myself. It cost just under $200 US in those days. I put 100,000 miles on that system with no rust-out and it is still going strong. Something came loose inside the rear muffler after several years and began to rattle. The Volvo dealer gave me a new muffler with no questions asked because of the lifetime warranty. A good deal! This isn't a bad do-it yourself project except for the pain of getting the old sustem off and dealing with the crud which falls on your face. Wear eye protection!