Have a problem with 1996 EF Futura six 180,000 klms. Seems as though a tiny amount of oil is making its way into the cooling system. When I remove the radiator cap a dark brown oily sludge has accumulated under the cap, clean it off and is back there again on next check. Have dropped oil from sump and no signs at all of any water in the oil, so it seems as though oil is getting into cooling system but no water going the other way. Have also noticed that engine is using very small amount of oil and this only started when sludge appeared. Any suggestions will be gratefully accepted. Car does not run hot at all even with air con running, gauge. Thanks