I JUST GOT BACK FROM THE MIDAS SHOP THAT BROKE MY MASTER CYLANDER ON MY 300E.(WHICH THEY ARE PAYING TO HAVE REPLACED) THEY SAID THE FRONT BRAKES WORKED FINE BUT THE REARS DID NOT AND THE PEDAL FELT A LITTLE SPONGY.
SO THEY TOOK APART THE MASTER CYL. ANREALIZED THEY BROKE IT. HOPEFULLY THIS INFO HELPS YOU OUT ON YOUR CAR.