So to clerify, you bled the brakes, topped the resevoir, test drove, the light came on, the level was then low, but no leaks found? the fluid must go somewhere.. a few things to consider: in general a sudden new problem is a result of a recent work done. Purhaps a slightly stuck open bleeder? It's common for master cyls to fail just after a bleed job and heres why: when you press the brakes on a normal operating brake pedal, it doesn't go to the floor. therefore you are only using a portion of your master cylinder's travel. the part that never gets used gets debris and contaminates in it stuck to the cyl walls. An unsuspecting person bleeds his brakes by pressing the pedal to the floor, thereby pressing the cylinder's seal over that contaminated area and ruining the seal and creating an internal leak where the fluid bypasses inside causing a weak pedal or a sinking pedal. But this will not leak externally and loose the fluid. nor will it cause a brake light issue also.. your rear wheel cylinders can leak inside the drum where you won't find fluid leakage untill you pull the drums. all i've got for now.. G.L.