My slave cylinder has been slowly losing fluid for years now, usually I just top it off ocassionally and it's okay. But now it lost it's charge of fluid over just a few days this time, I need to spring into action.

Ebay has a lot of choices, rangibg from $69 to $150. That's one way to go.

Is it worth trying to rebuild the one I have or Is there a good reason not to?

I've done brake cylinders before, I'd just need a kit.

How about the clutch master cylinder, not sure if it's leaking although the paint on the inner fender, just below it, is missing. I don't see anything in the way of fluid inside the car and the
inner fender doesn't seem wet. The slave cylinder is definitely damp though.