Brake Master Cylinder problems of the 2007 Lincoln MKX

I have been having issues with my breaks being extremely hard to press and at times not hardly working at all and when engaged it makes a hissing sound and I have come across bringing it to the shop it is the master cylinder for the breaks and or the break booster and then came acrossed my year of this vehicle has a recall on these things so I need to know about how to get these things fixed under the recall.

While our 2007 Lincoln Mkx was standing still, pressure was applied to the brake pedal and it went to the floor. I tried it several times over the next few days with the same result. Took it into the dealer, dealer said it was normal. I objected to that comment. On further investigation by the dealer, they said it was the master cylinder. They did replace the master cylinder. I got into the vehicle, pressed on the brake pedal, thought it felt funny, complained again to the dealer. They said they would give me a test drive with the same type of vehicle. Before that happened, the mechanic came out, got in my vehicle, pushed down on the brake pedal, which again went to the floor. His statement was huh?, must be in the vacuum system. That system is in the process of being replaced. Will keep everyone posted in the next few days.