Cork is a impermeable natural material and will not soak up enough grease to keep them from drying out.The "life" of a cork gasket or seal is aproximatley 15 years under ideal conditions.
The good news is that cork has a high elsticity and is very dense and thus presents itself as a good cushion for the elliptical springs on your truck as they move on the shackle pins.
Keep your shackles well greased and oil the exposed cork each time you grease the shackles.The oil will act as a barrier between the weather elements,road dust and grime and your cork seals.
Hope this helps.Hobert
