when your clutch looses all pressure, and when you check out the slave cyl its pissing out black brakefluid, can the slave cyl be rebuilt, or do you need to get a new one?

Most people just replace them with new or reman ones since the replacements are so cheap, under 25 bucks.

There used to be rebuild kits for the slave, but I wouldn't bother unless you wanted to rebuild the old one after you replace it for a spare. Even with a rebuild kit, there's always the possibility that what you have won't be in good enough shape to rebuild and last for long.

By the sounds of the color of the fluid, you definately want to flush out the system thoroughly, and if it's been like that for a while, the possibility of moisture in the system, would likely be the reason the slave failed in the first place.