I own 1 C25 pistol.
Have you also taken heed of the guidance regarding steel CO2 cylinders ?

CO2- gas cylinder – Steel design
After 10 years the CO2 - gas cylinders made out of steel must be examined by the manufacturer. During
the in house examination the steel CO2 - gas cylinders are inspected for corrosion not visible on the
outside. If there is no corrosion the CO2 -gas cylinder are proof pressure retested and provided with new
seals as well as marked with new test datum for a fee.
If there is corrosion or the CO2 - gas cylinder fails the proof pressure retest, the cylinder will be disposed
of without any risk. In this case the customer will be inform by FEINWERKBAU that the CO2 – gas cylinder
can not be used anymore without risk.