Classic/Antique Car Repair: Master cylinder, wheel cylinders, master cylinder

Question
I have a 1940 Hudson 2 door sedan. The car has been sitting mostly for the past couple of years. I noticed about a year ago that the brake peddle was low to the floor so I checked the master cylinder and it was low on fluid. I filled the master cylinder and then bled the brakes. That brought the peddle  up to full position. I drove the car and the brakes seem fine.

I noticed the other day that the peddle is low again. There does not seem to be a leak I never see any liquid on the floor. Could the fluid be evaporating?

Thanks,

Marvin

Answer
Brake fluid is an alcohol base and as a result it will do two things. It will absorb moisture out of the air and become gummy and it will evaporate. Also after sitting for a while the rubbers on the wheel cylinders and the master cylinder will loose their seal with the cylinder bore and weep out fluid and let air into the system.