Do you have any information to support this? As far as I know, there are no seals (at least rubber seals) inside a Swagelok metering valve.
Also, CO2 (the gas) would only be corrosive if there was moisture inside the metering valve, at which point, you would have other things to worry about before the CO2.
Finally, I believe there are many people that use other needle valves that do not have these Vitron seals, and they have lasted for more than 3 years.
old post.... but http://www.swagelok.com/downloads/we.../MS-01-142.pdf
clearly shows orings inside the swagelok valves
All but the HP valve have it.