In the M6 the brake pedal has gone soft & I am stumped as to why this is happening.

1. The first time it did it was just after I bought it, the pedal was soft & it failed the NCT for excessive brake pedal travel. A brake bleed was completed & it was fine for about two weeks.

2. Then it went soft again, about two weeks after the brake bleed was completed, again with pedal getting soft & the pedal travel is ridiculous. It was diagnosed as a defective master cylinder. The master cylinder was replaced and everything was good....for about two weeks.

3. So after two weeks with a new master cylinder it then was left in for another brake bleed & without any driving (it was in the dealer's compound) the pedal again went soft after a brake bleed.

4. This time the issue was diagnosed as a defective Servo. So the servo was replaced.

Here were are again about 2 weeks after that & the fucking pedal is soft again!

Anybody got any ideas as to why this in happening? The dealer doesn't seem to be doing a great job so far at identifying root cause but maybe it is just one of those hard to trace issues. The car is under warranty, while it is good that I am not being hit in the pocket for the work I would really rather just have the car fixed & be able to drive it. It's spent nearly 25% of my ownership in the dealers, brakes are not rocket science stuff either so the whole thing is getting frustrating.

Any help appreciated.

After each "fix" the pedal feels great for a week or so, and there's no leaks. It is wrecking my head at the minute.