The reason my 610 was taken off the road was half pedal travel on the brakes. It was thought to be the master cylinder and one was sourced from Simon Auto for 400 Euro's

With the ignition turned off I have a pedal, with it on I get the half pedal of travel. Question is out of anyone's experience does this point to the master cylinder (there seems to be no fluid loss in the bottle or sign of seepage around the cylinder). Or could it be the servo or a hose or something.
Anyone have any thoughts?