Had my A3 s-line serviced in August full hit brake fluid the lot . It came back with a spongy brake pedal took it back they bled the system again put more back in, the pedal was still spongy they diagnosed a master cylinder issue. It's been in the workshop now 2 days had two new master cylinders fitted at no extra cost to myself . It is a vw audi specialist garage and they havnt got a clue. They have pressure tested all the lines and checked for air blockages and split hoses etc but still cant tell me what the issue is . They told me to take to a main dealer but loathed to pay those prices . Any ideas please !!!