Brake Hoses, Lines/piping, And Fittings problems of the 2007 Mercury Milan

My car has on several occasions lost brake pressure after going over a bump or some hard road conditions. The first time it happened I had my brakes changed because I thought they were not good. The shop, firestone (los angeles, CA) made several attempts to get rid of the softness and going to the floor half way, but not until they bled the brakes for the 2nd time did it seems to work. Second time I was in mexico and the brakes were great - then I went over a large speed bump and my brakes all of a sudden went completely soft. I took it to a shop and they said the brakes were fine. They bleed the brakes and things seemed good again. The third time it happened I went over a pothole and again the brakes went from good to totally soft again. I took the car to marina Ford dealership and they told me that it was the hydraulic control unit and told me that it would be a $1,600 repair. I was shocked and told them I think there is something terribly wrong with this unit because I have gone through a lot of trouble with these cars brakes. They said they can fix it, but I didn't have $1,600 at the time to spend. So I bleed the brakes myself and changed the rotors and pads myself. After three times bleeding all four brake lines - it seemed good again, but when I am at a long light the brakes start to go down to about half way and the car starts slowing moving until I pump the brakes. I really think Ford should replace this. It is dangerous and it is their error I believe. It is a lemon part. They told me that some brake fluid gets stuck in the hcu after a perceived abs event. Then it should come back through the unit again, but it doesn't and get stuck in there and that is why the brakes are soft. This sounds to me like a faulty part, but they won't fix it unless I give them $1,600! I can't change it myself, it requires that there is a computer reset and only Ford has that.