Thanks, after looking under the hood again I can see the parts. My confusion partly because I didn't realize that the giant cylinder behind the master cylinder was the brake booster. I thought it was the housing, and the brake booster was somewhere inside of it.

Assuming that the booster, and not the check valves, are to blame, I'll be replacing the booster. The FAQ says:

"Replacing the Booster. [Paul Golden] Replacing the booster takes about an hour and a half or less. Remove four nuts on the inside of firewall, the brake pin, two nuts for the master cylinder and gently pull the m/c out of the way. The booster comes out at a slight angle"

When it says "pull the m/c out of the way", am I going to have to remove the master cylinder? I don't see how I could move the MC without disconnecting all the brakes lines that connect to it. If I have to do that, I'll have to bleed the entire brake system, right?

I just want to make sure I don't make it any harder than necessary.

Thanks,
Miceh