If its upfront the caliper seal on that side is worned out
January, 15, 2013 AT 10:35 PM
Spray the entire area with brake parts cleaner. When it evaporates, have a helper slowly push the brake pedal so you can see where the brake fluid is coming from. Suspect the steel line in the area where road salt and water spray onto it from the tire.
It's very important to tell the person pushing the brake pedal to never ever push it more than half way to the floor. Doing so can damage the master cylinder.