I am having problems with the brakes on my 2010 Mercedes-Benz A-Class A160 CDi. For the first 18 months the brakes worked OK, but then (when stationary and holding the car on the footbrake) the pedal sinks slowly to the floor. It can then be pumped to retain the brake pressure.

At the annual service in December I reported the fault and the brake fluid was changed and the brakes were restored to the original state. Now the problem has returned. The dealer has changed the fluid again, but it has not rectified the problem.

The service manager told me that all A-Class diesel cars are like this, but the car did not have this problem to start with and I now feel very unsafe driving this car. How can hydraulic fluid continue to be compressed?