well, all the GX's have KDSS, so the special service tool (SST) is present at a lexus shop. Whether or not they would help you out is a different story.
The KDSS does move around all over the place. Check out this great video from a forum member (check out around 2:56):
YouTube
What about the front piston is knocking? Is it the connection to the frame at the top, or the connection to the swaybar? Have you replaced the swaybar bushings and the KDSS bushings? They are all very cheap and easy to replace on the ground, in the driveway
Is the cylinder (front or rear?) leaking?
