Back when I still collected milsurp, I ended up finding unassembled 3M M40A1 gas masks for $80 in a DRMO auction. I got two extra filters for it, opened the parts, read all the manuals I could, and assembled it with an earlier gen quick doff hood. All three filters' 10 year expiration date hit in 2023. Would these still be useful against RCA, or trash them, don't risk it at this point? All are still in their original plastic sealed containers and have never been cracked open.