I'm helping my father put back together this rare beauty of a truck but we have encountered a problem it seems the brakes arent getting any power assist and are too hard to push the pedal down all the way. Replaced new drums, pads, no leaks in the line and bled them, new master cylinder, new booster/plunger(rebuilt one), checked the vacuum pressure with my finger-not recomended...lol drew blood just underneath my skin but not painful. Checked the O-ring from the vacuum pump unit it is worn and cracked. Right now I'm ordering a new o-ring seal. I can't figure it out though.Could this little seal be the problem? The plunger is extended out all of the way I didn't do any adjustment before the install. Thanks in advance for any input and thanks for the forum.