I have a 1950s sink with an old technology in the pop-up stopper. The trip is a rotates rather than lifts. The pin fits into a cylinder with a cut out for the pin. (I've attached a PDF with a mock-up of the cylindar/pin system.)
The pin does not lift the cylinder anymore. It seems that the pin is not moving vertically as much as it should. There is no way to replace the stopper with the current technology without replacing the entire sink.
Any suggestions on fixing this…rather than purchasing a new sink?