The oil is held with seals that fit in the tube. The gaiter is there to keep the dust and road dirt out of the exposed part of the sliding tube. What actually happens is that the seals wear out with time, allowing the oil to seep out, that comes in contact with the gaiter and makes it deteriorate.
So you need to replace the seals, as well as the gaiter. Until you will be able to do this, you can add oil to the tube (it only takes a small amount of oil anyway, you don't fill to the top) to stop it working completely dry.