I will test the check valve at the pump fitting instead of at the first joint, now that I have a metric 6mm hex bit, because I am curious about the check valve, but I think I would be farther ahead with a new vacuum pump also. I am getting a squeak, squeal noise that soundes like a water pump going out if you know what I mean. Could a vacuum pump going out sound similar? I didn't have a mitty vac to measure the pump a couple of weeks ago, but I pulled the line at the same place, first joint, and stuck my thumb over the end and I had good vacuum. Did the same thing yesterday when I was trying to get it to shut off and I had very little vacuum. I had the manual shut off switch adjusted properly, I had tried it a number of times, but yesterday it wouldn't work enough to shut it off. Had to put it in gear, have the wife push the lever, and I had to smother it to get it shut off. Whew!