You may be past this point, but the first thing I would to is a little trouble shooting. Have you tried removing the lines leaving the master cylender and installing plugs, and stepping on the brake peddle? If you are questioning the master cylender as a unit this will disable the rest of the system so you know for sure that the leak in internal. the peddle should not move because there is no where for the fluid to move to. If it moves at all then one of the seals in the master cylender is bad.

hope that helps, good luck

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