Intermittent brake issue

[fabiamk2]

I have a 2012 skoda fabia 1.2 greenline diesel

 

The car has developed a fault whereby randomly every few trips the brake pedal will be go randomly very soft and brake power reduced and once pressed again straight after it firms up. Its been doing this once every few trips. No brake fluid loss and have tried pumping brakes whilst the car is off and it holds pressure. My local garage don't want to touch the car anymore. Obviously as its brakes it's not something I want to leave but due to how intermittent it is its baffling me.

 

Anyone had this issue before. Was thinking maybe a sticking caliper due to how intermittent it is? Anyone got any advice or had similar? I did once have the ABS light come on when a tyre pressure sensor came on due to rim leak but once tyre pumped up it went off and hasn't been seen since so no idea if that's anything to do with it.

[UrbanPanzer]

Sounds like either a failing master cylinder OR a vacuum leak, be worth checking ALL rigid nylon vacuum pipes as they can split and intermittently leak particularly where they are pressed onto fittings / connections.

 

Out of pure interest, why does your local "garage" not want to touch it anymore ? have they divulged into bacon butties instead !!