I have a master cylinder that needs rebuilt. If it is excessively pitted, should I consider sleeving it? White Post Restorations sleeves with brass. Karp's Brake Service sleeves with 304 stainless steel. Anyone have experience with either of these companies? Any other recommendations?

Yes, it is the original master cylinder. Has never been rebuilt. My parents bought the car new in 1973 and I've wrenched on it ever since. Master cylinder still works but has a slow leak. I would like to rebuild the original if possible, however, the bore may be too pitted to save. Sleeving seems to be a good option but would like to get some opinions from others. White Post has advertised brass sleeving for years, but I saw this recent ad for Karp's and stainless steel sleeving. Any advice?

I use Brake and Equipment warehouse in Minneapolis and they use steel sleeves. Never had a problem with the master cylinders after I've rebuilt them and installed on a car, the one on my convertible has been on there is coming up on 5 years since I had it sleeved.
If the exterior of your original master cylinder and the reservoir are in good shape, I'd say go ahead and have your bore sleeved.