There is a method of replacing the oil in those shocks. Do a search and you'll find a thread by a man that used to work for Progressive Suspension. As I recall he advised the correct amount of oil for a couple of different length air shocks. Do not just guess and be careful of the post recommended by cts1950 - there's just too much guesswork involved there. Those shocks need a prescribed amount of oil to work properly. You adjust the damping with different weight oils - NOT different oil levels.