Hello Bee, I went through the same thing and got a lot of good advice on this site, which led me to remove the hydrovac on my 58 Spartan and have it professionally rebuilt. Note that the unit I had on my truck was a brand new old stock unit from a circa 1980 truck which I adapted onto my truck, but it leaked just enough that it caused that chronic low pedal (the leak was internal, so difficult to assess). There could be other problems, including the master cyl and shoe adjustment (which needs to be VERY tight - honestly, I tightened mine tighter than the specs, based on Mike B.'s recommendation). But considering that there are MANY reports of booster issues, I would be suspicious of it.
