I've used an old air filter before (made in 1998 in 2009) but I just purchased an old Purolator Premium Plus L20195 at a thrift store that has a copyright on it of 1997. It's in the older white box, before Bosch and Hummel/Mann acquired them. I'm guessing it's at least 10 years old, but it looks perfectly fine. I don't see any rust by looking at it. No dents or scratches, think it's safe to use? I haven't used an oil filter that was more than 5 years old.