An anodized finish is oxidation. Don't worry about any aluminum. However, the screws and steel internals can rust.
As for the 12 gram problem, my first thought was that the pierce pin seal was missing. It's less likely on a platform like this, more likely on bucket changers, as they are frequently opened with CO2 in the cartridge and rather quickly; they can blow off. If that happens it will leak from around the pierce pin no matter how tight it is.
However since you said it was coming out the top of the valve, I would guess a poppet/seal/oring is bad or unseated. If its still happening, you will have to open it up.