I was told last November when I got an oil change that I needed a new muffler soon. I brought my car in today to have the mechanics examine it so they could order the part, and they discovered a giant hole in something called the "B-Pipe" that sits right underneath the driver's seat.
The repair is gonna run $680 (ouch) but more horrifying is that there was a very real possibility that I could have experienced carbon monoxide poisoning, especially if I was stopped in a traffic jam. 100 ppm is the maximum safe amount of CO that a human can be exposed to, and with basically no exhaust filtration, a much deadlier amount could have been seeping up from underneath my car. We were stuck in traffic down in FL while we were on vacation. I'm stopped in busy traffic every morning on my short commute. I've probably been breathing in elevated levels of CO for months without realizing it.
Until the repair is done, I've been warned to crack a window any time I'm stopped at a traffic light.
Well, at least I have something to blame my short term memory problems on these days.