Need a replacement shock. What kind?

[pwd]

So my rear shock appears to be leaking fluid or something. I am not surprised because the bike is over 15 years old and the roads hear have some nasty pot-holes. I would like to get a new rear shock as I am sure this old one is not worth servicing as it is an older style etc...
I don't know much about rear shocks, but I have had no progress trying to find what type of shock this is, does anyone know what kind of shock would work here?:

 

[Ykick]

It should be rebuildable. Have you checked the Rock Shox website for technical info/parts? Park tool offers some rebuild help too:

http://www.parktool.com/blog/repair-help/rockshox-rear-shock-service-monarch-4-2

Comparable shock will be fairly expensive to replace IMO.

 

[Drunkskunk]

The Rock Shok should be rebuildable, but it's old school tech. you can improve the ride by going to a more modern shock, with dampening and rebound adjustments.

You will need to know a few things to replace the shock.
The length of the shock measured from the center of each mounting bolt, when the back wheel is off the ground.

The rating of the spring. It should say on it someplace, but you can experiment with different springs to find one you like. You could also go with an air shock instead. that would eliminate the need for spring selection, but up the maintenance as you would need to keep up with the air pressure in the shock.

The width of the mount.

DNM makes cheap but decent shocks that would be an improvement.
For the best ride, you can try a Fox Vanilla or a Marzocchi Roco.