Master cylinder puking fluid

My master cylinder looks like it is leaking fluid from the cover, also when you check fluid levels after a couple days driving around, the front chamber will be empty and the back looks pretty low, can fill back up with fluid, brakes feel excellent, but it will puke fluid from the lid by the loooks of it. Any one else ever have this problem. Replaced the master cylinder but still doing it. Brakes are 12x2 1/2 rear drum and 11 3/4 front. I havn't installed my aftermarket proportioning valve and the rest of the brake system is stock albiet all new pieces. I just don't get it. Is this a cover leakage problem or is it actually pumping the fluid out due to a bad combonation valve? Anybody, thoughts, ideas?