RST58 MTB rear shock rebuild

This is a coil shock with hydraulic damping with adjustable rebound damping as well as a lockout. When I got the damper there was absolutely no compression damping, the rebound damping was fully functional. I couldn't find any information on this RST 58 damper, also tried contacting RST Europe but didn't get any response. So I searched for other damperes with a similar design to get an idea of how its put together.  Rockshox Super Deluxe seems similar in design and Vincent had dismantled one and posted a photo with all the parts, which helped me a lot: http://www.retrobike.co.uk/forum/viewtopic.php?t=178217 thanks for that!

I went on and disassembled the shock into pieces, shown in the picture below:

The root cause was obviously a broken O-ring of the upper reservoir cap. The compression side air and fluid escaped through the hole in the seal. Another problem was a worn rod bushing which caused the shaft to leak. I measured all of the installed o-rings, went on and replaced most of them. After replacing the bushing and seling rings I put the parts together and filled 5W fully synthetic shock oil through the hole where the compression damping valve screws in (note that the thread of the valve base is left-handed) I did several rounds of filling oil into the small aperture and moving the piston back and forth to purge air out. I filled as much oil as I could, now the shock works perfectly.