Master Cylinder Leak

[YukonJack]

Put disc brakes on my 47 Plymouth years ago and used the stock master cylinder with a Wilwood residual pressure valve inline. This has worked for years but not an ideal set up. The last couple of years the car doesn't get driven much and after sitting a while I have a puddle of brake fluid on the floor under the master cylinder. I suspect the fluid is draining out the calipers to the master cylinder and then out of the vent holes in the cap. The outside of the master cylinder is wet. I would think the residual pressure valve would prevent this from happening. Any ideas on what could be causing this? 

[Sniper]

There is no perfect sealed system, stuff leaks.  the residual pressure valves will leak by over time. 

[Doug&Deb]

Have you removed the residual valve from the master cylinder? I’m running a Scarebird kit on my Coronet with the original master cylinder. I removed the valve from the master cylinder and added two inline valves to the front and back. Two pounds to the front and ten pounds to the rear. I haven’t had any problems yet in close to 10,000 miles. Perhaps your master cylinder has finally failed from age. A rebuild may fix the problem.

[Adam H P15 D30]

I also removed the internal check valve but I did not add any residual pressure valves in line.  Been that way for many years and I never leak any brake fluid even if it sits for months.  Perfect pedal always even the first apply after sitting.