I fixed a problem with my RS Revs last week. The compression adjuster was only turning half way from fully open and not achieving lockout. Whipping out the compression unit revealed the top O ring had “prolapsed” for want of a better term and was fouling the adjuster.
To fix I had to remove the top of the commpression stack. This is a left hand thread, but once off the troublesome O ring could be removed. It looked fubared, it had a big blister where it had been pushed through a gap, but once the pressure was off it relaxed back to a perfect doughnut. Since I didn’t have a replacement at the time I refitted it and its done 90 miles since with no problems.
Check on here for other posts which have pictures of the compression unit in bits and this gobbldygook will makes sense.
Just found the post that helped me out here