If it's out of warranty a better option exists now. Use a Chair Saver Kit to fix a sinking gas lift on an adjustable office chair. No tools required, no need to take the chair apart and installs in under a minute. Keeps the proper ergonomic height for a user, and permanently fixes the sinking issue. 20 times less expensive than buying a new ergonomic office chair, or trying to find the right cylinder and install it yourself. You can get one at Chair Saver | Fix Your Sinking Office Chair. Keep using you chair for years to come without sinking.