Two minutes to fix it!
First remove the ink sac from the pen, just gently pull it off;
Then separate the black part (push-pull rod part) and the transparent part of the ink, the transparent part has a card slot on the orientation of the push-pull rod, and only two parts are folded in half at a small Angle (not too large, so as not to damage).
Secondly, the rubber ring is pushed out with matchsticks and installed in the card slot on the push rod, taking care not to lose the small steel ball;
Finally, put the small steel ball into the ink sac, push the piston into the ink sac, and the protruding part of the card slot is flush with the push rod, push tightly, and then install the ink sac on the pen. OK! Note: Do not pull the rod to the end when the ink sac is absorbing ink! Otherwise, the rubber ring will fall off the tie rod.