2011 Ford Edge brake mystery

I own a 2011 Ford Edge and I’m having an extremely dangerous brake problem. Occasionally the brake pedal goes to the floorboard and doesn’t stop the vehicle. I have taken the Edge to a Ford Garage and Firestone several times and no one can find a problem as it is a random. The brake booster has been changed as has the master cylinder. There is a very expensive part that can be changed, but Ford states there is only around a 50% chance that it might fix the problem. Do you have a solution? I see on-line that this is a common problem.

If you have no air or leaks, the problem could be sticking master cylinder or faulty valves in the ABS unit.

Has road salt compromised your steel brake lines . . . ?

or do you live near the ocean . . . the salty sea breeze will also do a number on brake lines