You need a rebuild likely including re-sleeve. I would go with brass sleeve rather than SS especily if you opt for the DOT 5 fluid. It will not corrode like the cast iron and costs a lot less than the stainless sleeve operation will cost. Probably last forever. Apple Hydrauics does good work at a fair price and have a web site with prices. I replaced my brake system and installed silicone dot 5 fluid but nearly everything was replaced except for the combination valve, proportioning valve, and the rear wheel cylinders. You should follow the directions that come with the fluid. Change the rubber lines for sure as they have dot 3 soaked into them. Good luck,
P.S.- LOTS of people argue this silicone fluid thing to death but if you like to store the car and/or go for long pieriods of time without doing a lot of maintenance, go with the silicone dot 5.