I have offered to help an aging relative sell a Umarex 850 Air magnum rifle in .22 flavour.

It appears to be in good general condition however it apparently leaks where the CO2 canister screws in.

Have any of you had the same issues and if so, is it a simple seal replacement?

Once fixed has any one got an idea of what its worth.......Its not got a spring in it or any wood either so its not my cup of tea at all

Many thanks in advance.

Cheers Steve