If you've been loosing fluid from the "front reservoir",. meaning the one closest the front of the car,, then you've got a leak in the rear wheel system.. Often a steel brake line will rust up in the chasis,, you should be able to detect a wet spot on the frame,, or you may have blown out a rear wheel cyl .. If you're loosing fluid in the "front brake reservoir" (rear most reservoir),, the front brake system has problem,, and may be as previous post,, check for wet spots.. hope it helps
