If the seatpost has developed a significant side to side wiggle, your shims need replaced. The shims are (item #42) on the inside tube.
You can purchase a rebuild from our website, and send your post back to us. We will install new cable, housing, bushing, and plastic shims (#42) for $15. You might specify that your post has developed significant twisting wiggle. We generally have the post back in the mail to you within two days.
If you would like to install the shims (item#42) yourself, you can order the shims from the products replacement parts page. The procedure is simple, but a little tricky. We highly recommend ordering a couple sets of the shims (as they are easily ruined which makes the post sticky up/down) and watching the video tutorial on changing the shims if you decide to do it yourself.