Brake Abs Warning Light problems of the 2008 Mercury Milan

My abs light has been on ever since I had to slam on my brakes. Both of my front tires locked up almost causing me to rear-end someone on the highway. The pedal felt weird but it could still stop. My abs light is still on.

Several years back, I had a near failure of my brakes when rolling down a hill toward a right turn at the bottom. ( I think in retrospect that because of my hitting some bumpy patches on the turn lane the brakes attempted to actuate abs). I had sufficient braking, pedal to the floor, to roll to a stop. Popping the hood, I found the cap on the brakes fluid reservoir was ajar. I refitted it and found that the brakes worked normally. (in retrospect, I do not believe that a "failure" occurred in the reservoir cap, but was instead a consequence of other malfunctions in the system. Some time later, I had another failure, which nearly resulted in a crash. I limped to garnet Ford, and had repairs done, totaling about $1200. The cautionary I received from the service rep was foreboding: replacement of the master cylinder may not fix the problem. They then claimed that the repair was sufficient. (in retrospect, I should have been at the least taking this action then and there: an automobile with only 35,000 miles on it ought not have dangerous and defective brakes). Last month I had to have brakes repaired, as a result of problems stemming from my wife driving the vehicle, and experiencing much the same thing as had occurred to me the first incident. Front rotors and pads were serviced, but that did not fix the problem. Now my abs warning light is intermittently on, and I am getting a roughness to braking as if the front brakes are worn down: they are not. I am returning to the mechanic with this problem. I do not know what the outcome will be, but it is suggestive of a built-in defect, which is tremendously hazardous, and irresponsible of Ford to ignore this defect.