I just bought the Britax Marathon about one month ago for my 9 month old daughter and am hoping to use it for our future children as well. I do think; however, that we should stop using the carseat after the manufacturer's recommended "expiration date". This is just my opinion, because of course, maybe the carseat would function just as well after the expiration date, but maybe it wouldn't. If the manufacturer can't guarantee it's safety, I wouldn't be comfortable using it. I can see how the plastic might be less effective/sturdy after 6 years in the car and being exposed to hot and freezing temperatures on and off again and again each season. I believe that I read somewhere that over time and with extreme temperature fluctuations, tiny micro-cracks can form in the plastic.