Thanks all for the advice. I'll see what the cylinders look like and decide from there whether to replace or rebuild. I priced them out at an auto parts store over the weekend and they were $16 a piece for regular or $20 for what they called premium. I'll have to check out the manufacturer.

How do you flush the system? I assume it means you want to force brake fluid through all the lines to clean them out? I'm expecting to have to replace some of the brake lines too, not that I've found any leaks in them yet but I'll probably bugger some of them up working on everything.