hi there - i have an old (c. 1915-ish) wall-mounted enamelled sink with a broken stopper. the stopper is a push-button type that normally would be removed by twisting counter-clockwise and unscrewing; however, it seems to have seized and is listing at an angle so i assume has been bent somehow. what now? can someone explain the mechanics of this type of stopper further and what my next steps should be? is there more than one type/style of push-button stopper?

thanks for any & all help on this topic.