depends on how old. The old ones, 30+ years, had leather seals. If they sat fora long time they dried out. I have taken them apart and soaked the leather overnight in oil. Sometimes it got them to work, unless the leather is torn of course. The newer ones use a combo of rubber, teflon and or ceramic. You can find them at most industrial supply houses. Graingers has a quite a selection of seals, o-rings and back up rings in any sizes for about $10

good luck.
John