@toyochan I second this comment, copper tubes can only go so far when compressed. Steel tubes will have more reusability since they are harder to compress or flatten. If this doesn't work, you can verify that the flared tube matches with the taper angle of the splitter and the interface between hardline and flexible line. Working on old cars can be stressing especially when encountered with troubles like this but I admire your ability to continue and not give up. Good luck!