Gently squeeze the assembly together with the sight leaves & pin in place.
You have to put friction on the leaves from the sides to keep them in position,,a light press fit into the base itself.
Sometimes it easier to do w/o the leaves & pins in place,,but it's also very easy to go too far this way.

It's still not the best system and will again wear and get loose as they are pivoted back and forth. But it will last much longer than a tight fitting pivot pin.

Maybe if you magnetize the whole thing the leaves will stay put in the down position. Doesn't do much for long range work though..