Leaky adjustable proportioning valve

Thanks for all of the information, i spoke with john down here in whitehall pa at whitehall auto parts, he very good with repairs, he told me to try using permatex high temp. Sealant it is good for hydralic parts, i was going to give that a try, question- if i put something [plastic/aluinum foil] under the lid of the master cylinder cover will that make a vaccum and hold back the brake fluid? Or do i have to drain the resiover to stop the brake fluid from leaking out on to the valve connection??
Dave