Scout II Lost Power Brakes

The Orange 1979 Scout II , which serves as my summer Scout, lost power brakes last week. The car would still stop if you stood on the pedal, but had no power brake assist. The first step in diagnosing the problem was to look for missing brake fluid. I opened the lid to the master cylinder and noticed that the smaller (rear) reservoir was half empty. The rear reservoir pushes fluid into the front calipers, so I inspected the area around each caliper for brake fluid, but found no leaks. I knew that the fluid was going somewhere, so I pulled the brake master cylinder off of the brake booster to inspect the main piston seal. There was evidence that fluid had made its way past the seal and was slowly leaking by the cylinder. This small fluid leak necessitated my changing of the master cylinder, but did not explain my main problem, a lack of power brakes! The next thing that I checked was that my piece of fuel line that I had used to run vacuum from the Holley 2300 2 bbl carburetor to the brake booster was solid and intact, which it was. Next I removed the booster vacuum check valve and line and connected a vacuum tester to the booster to test the diaphragm.  I applied 75 psi and watched the vacuum gauge to look for any movement in the needle, the needle stood still. The only other part that I thought might be malfunctioning was the check-valve between the carburetor and the booster. I swapped the check valve with a new one reassembled the brakes with a new master cylinder, bench bled the cylinder and reconnected the lines. The check valve was the culprit, the brakes worked great! It was nice to know the I had caught my slow master cylinder leak in the process to avoid a future accident.