I have bought a MityVac and hope to use it, but not until I've corrected whatever it is that is amiss.

I really think now that my master brake cylinder's primary stage is likely worn and only pressurizes braking action now in the secondary, or emergancy back-up stage.

I am going to take the master out and have a look at the piston seals and cylinder for corrosion etc. The outside condition looks brand new and is deceiving! BB