Neon, it seems you have anxiety about repairing a cartridge that at the moment sounds “glorious”. Unless something has changed since you initiated this thread. If not, why not just relax and enjoy?
Factoid: two years ago while cartridge shopping in Tokyo I saw an Ikeda cartridge for sale that also had a kanji symbol on its side. I can’t say whether it’s the same symbol on your sample, but it’s evidence that the kanji doesn’t necessarily indicate a vintage model. However the cartridge was very expensive, so you can feel good about that.
Factoid: two years ago while cartridge shopping in Tokyo I saw an Ikeda cartridge for sale that also had a kanji symbol on its side. I can’t say whether it’s the same symbol on your sample, but it’s evidence that the kanji doesn’t necessarily indicate a vintage model. However the cartridge was very expensive, so you can feel good about that.