I have, on occasion, cut a short length of thin brass tubing to slip over the pin and take up the slack (my old K2 seat got like that). I got the brass tube at the hardware store (thin stuff), slit it to fit the pin (it wasn't metric) and sanded the pin clean and applied lacquer thinner: then I made sure it would slide into the slit tube and super-glued it on. I never moved in 10 years of riding, either! I used a Dremel with a cutting wheel to slit it.