Need Help Troubleshooting Brake Troubles

I would separate the master from the booster and see how it works. Studs are long enough to get a good gap there. I'm no expert but seems to me the booster would work right, pedal would return, even if there was no fluid or vacuum. I have seen a couple of bad valves. One that would lock up just the right rear wheel of a front wheel drive car with light pedal effort. The pedal always returned though.