Rock Shox Reverb Stealth with Connectamajig. Spares or Repair.
 
30.9mm Diameter.
390mm Length.
125mm Drop.

The seat post is suffering from what most Reverbs go through at some point, and drops about 15mm when you sit on it.

From what I've read it needs a full service with new seals and bleed. Some tools (that came with it) are included.

Other than that the hose has some nicks in the outer casing (from the terrible internal routing in my frame) but this is only cosmetic.