JUST FITTED A FULL SET OF SAMCO COOLENT HOSES AND EVER SINCE IT OVER HEATS.WHEN I REMOVED THE OLD HOSES THEY WERE FULL OF OILY GUNGE SO I HAVE FLUSHED THE WHOLE SYSTEM RIGHT THROUGH SO THE WATER RUNS CLEAR.I HAVE FITTED A NEW THERMOSTAT,ELECTRIC FAN SWITCH AND HEADER TANK CAP.I FLUSHED THE SYSTEM AGAIN TODAY AND RE-FILLED AND YET IT STILL IS OVERHEATING I HAVE NOTICED THAT IT HAS A LIGHT FILM OF OILY GUNGE IN THE HEADER TANK AGAIN.HAS MY HEAD GASKET GONE OR IS IT SOMERT ELSE.ANY IDEA'S.???????????????