The Mégane II Owners' Club

Thanks in advance

I've got oil in header tank about an inch of gunk not losing any water or overheating and nothing on dipstick or around oil filler cap also a massive leak around thermostat housing and oil sensor switch. Is it head gasket or thermostat housing?

I'm having same problem except not sure where leak is from. Can oil enter coolant through thermostat housing? Top of header tank was about an inch thick in gunk but nothing in oil filler cap or dipstick.