Ok so I e-mailed two of them and this is the response I got from one...
Item: BABY CAR SEAT- BRITAX ROUNDABOUT MODEL 161 (280095611765)
This message was sent while the listing was active.
safna0 is the seller.
Hi. we contacted the retailer who we purchased the seat from. They said there is no expiration date on the chair. If the chair has not been in an accident and the parts are not frayed or breaking down, the chair is still fine for use. Please contact britax customer service if you have any other questions.
Details for item number: 280095611765
Item title: BABY CAR SEAT- BRITAX ROUNDABOUT MODEL 161
Item URL:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280095611765&sspagename=ADME:L:RTQ:US:1
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My response
I have contacted Britax in the past and it is planly written in there frequently asked questions that there seats should not be used longer then 6 years. You should contact Britax and ask. It may not have been in an accident but because of its age there can be unseen wear and tear.