Sounds like a good idea to go thru and replace flex lines, rebuild master and wheel cylinders and repair any steel lines that look bad, new shoes and drums. The hydrovac units are pretty durable so eliminate everything else first. I think the system is designed so that if the hydrovac unit doesn't operate, it is bypassed and the brakes will still operate off the master alone, although you may need to stand it. I think the hydrovac also has an intake air breather filter. They are usually mounted on the firewall on the pasenger side. It's a small oil bath filter. I'm guessing it allows the hyrovac unit to gulp clean air. Last resort, rebuild the hydrovacs. Brake specialty shop near me rebuilds them for about $300 clams so it ain't cheap. But what's a little thing like brakes?
