I can assure you that the reservoir does connect with the bore, otherwise there would be no brake fluid for the pistons to act on. Those Italians are clever but not that clever ;)
What probably happened, if you’re looking at an older brake system, is that moisture got into it and has oxidized the passages. If you see a bunch of white stuff in there it’s aluminum oxide. Older brake systems can be rebuilt but often it’s more effective in the long run to replace the components with new.
Also, are you using a brake bleeder or are you just trying to pour fluid into the screw on top? If you’re not familiar with these systems they can seem pretty foreign compared to automotive brakes but they really are simple. If you can find someone locally that’s been through a rebuild to help you that might be your best bet. Otherwise, if you’re trying to get brakes working on an older kart I’d suggest planning on going through everything as once the master gets corroded so will everything else.