disc drum master cylinder leaks to rear reservoir

[blazer2007]

I noticed my brake pedal was going further down than normal so checked the fluid and the fr. reservoir had filled the rear, so I took a turkey baster and took the fluid from the rear and filled up the fr., and was perfect ,no added fluid was needed. About a couple weeks the it did it again. So , is this a bad master or do I have a brake problem. Fr. pads are good and rear could use some new shoes soon.