CO2 rifle repair- presumed valve leak

[lukeatme]

Hi,

I have a Walther Lever action CO2 .177 rifle, which takes an 88gm CO2 cylinder.
Recently, when I tried to load a CO2 cartridge into it, it loaded successfully, but the gas immediately started leaking out of the barrel.
I haven't used the rifle in a while (I work in Bombay, the rifle stays in Calcutta), but I keep it well oiled and do basic maintenance on it whenever I'm in Calcutta.

Are there any gunsmiths who would be able to repair my rifle here in Calcutta?

Any advice/suggestions/help would be much appreciated.

Thanks,
lukeatme