A CO2 cartridge is leaking when installed in the gun

Seal exchange at Feinwerkbau P30

Hello everybody,

have a Feinwerkbau P30 which I bought a new cartridge from 10punkt9 last week, because the original cartridge has already expired for 10 years.

When I inserted the new cartridge, however, it blew the amount of air out of the cartridge in one fell swoop.

My shooting colleagues said it was either the seal in the gun, which has adapted to the original cartridge over the years and no longer moves itself due to its age.

Another said that the fit of the nipple of the new cartridge may be too small.

I then measured that with a slide gauge. It is smaller than the original cartridge by 0.14mm.

A working rubber seal would normally compensate for that I think?

Now my question:

Is it possible to replace the seal in the weapon that seals the cartridge when screwing it in, or is it absolutely necessary to use Feinwerkbau?

They would do it, but 200Eurons are already steep for a general overhaul of a P30.

Because I would have a suitable sealing rubber 7,0x2,0mm, but at the moment I'm still a little scared (despite manual skill and necessary tools) that goes a little wrong when dismantling the pressure reducer.

Maybe someone here has experience and can give me tips.