Could be a couple things. Brake master cylinder. You can take it off and take it apart fairly easily and clean it up. The seal can get a lot of build up especially on the bottom and start to leak through. Before you do that however is it for sure you brake master and not your clutch master cylinder which often looks like it is coming from the brake but is really coming down the clutch arm.
1980 CJ7 GM151 Bored out, Flat Top Pistons, Hedman Header, 2.5in Superlift springs, Extrem Shocks' 31 10.5 Mastercraft Courser MT tires on Allied MockLoc rims, Blazer heater upgrade.
2003 Liberty Renegade