I had leak in the same location, behind driver front wheel. Mine failed suddenly. Turns out the lines whent through an area where the plastic bottom protectors was holding water against the lines causing them to rust from the outside. My Local tech put in a patch.

I also have a failed master cylinder, but its not leaking. I have not yet bothered to replace it. At this point, i see no reason I should. Brakes work fine, just need a little extra travel.