I have a Britax Marathon that DS has been in since 2006. How do I find the expiration date? Someone once told me not to use a car seat beyond 5 years, is this accurate? I'm planning to buy him a booster soon to use on short trips in DH's truck, but would like to keep him in a 5 pt. in the main car as long as possible since he is VERY wiggly, but I really don't want to shell out for another Marathon in the next year, (although his shoulders are getting close to the top slot, so I may lose that battle anyway.) BTW, planning on probably getting either a Recaro Vivo, or Probooster for truck, and eventually transitioning it to the car when the time is right.