[FWDLK] 1955 Imperial Power Brakes

Here I am again with more questions. My wife and I took a ride in our 1955 Imperial yesterday. When turning into our friends drive way the car stopped as it should. No one was home so we decided to go to this other house just up the road a mile. Just as I was nearing the driveway, I applied the power brakes and to my surprise I had to jump on the brake pedal like never before. I went past the drive way and pulled into this turnaround and got stopped. The pedal would not push down with ease--very, very hard. So we drove with caution back home. Fortunately we were about 5 miles from home and not any traffic. I got it tucked away in our shop and this morning I got the manual out. I did as the manual said to check things out. Pump the pedal a few times to relieve any vacuum, Hold pressure on the pedal and start the engine. The pedal should have went down some--it didn't. Check the vacuum hose and check for vacuum. I replaced the hose and felt for vacuum. There was vacuum there as I put my finger over the hose. Check the check valve. I took the check valve off and took it apart and cleaned it. It did not seem to be bad. It also said of a broken or bent push rod. Of which I would need to disassemble the power brake booster. Any ideas as to what is going on with my brakes? And if I have to have the booster rebuilt where do I turn to. Or is this something I can rebuild myself with a kit. Or could it be the master cylinder seized up for some reason (just thought of this). They worked fine and then 2 minutes later up the road they didn't. Really weird to me. I did notice when I unscrewed the check valve, that there was still vacuum in the chamber the check valve mounts to.

Thank you all in advance for your insight and help.

Jack in Shinglehouse, PA 85* today