Bad booster?

I wish somebody sold kits to rebuild a booster. They are fairly simple inside and the Midland-Ross ones w/ a V-clamp are easy to disassemble (Bendix is tougher). Shipping the whole booster back and forth gets expensive, whereas a parts kit would be small. I think if one just had the rubber diaphragm, it could be replaced on the metal piston. I once cut thin neoprene sheet to make my own, but it didn't have the proper folds. It worked, but I scored a rebuilt booster cheap on rockauto so used that. Since, I found the leftover neoprene sheet stock cracked thru, so expect it won't last in the booster. A better rubber, formed correctly would be great. Otherwise, the only other part to replace is the "air valve", which is a packaged unit and can sometimes be found on ebay, and some sliding seals on the input shafts.