During slightly over one month I have had to top up the brake fluid reservoir twice on my Grand Voyager (2008 2.8 CRD) because the brake warning light has lit up - however I can not find any signs of leak anywhere.

In my opinion the brakes also need a little bit more pushing power then before. When the engine is not running the brake pedal slightly moves when pressed and stays at that position even when pressed harder just as it should.

But when the engine is running a quick brake pedal press works the same as above - but when pressed slowly it goes all the way down to the floor.

Has anyone a hint on what the problem might be?