Before you condemn the head gasket, check the water pump. I'm not sure if they have a witness hole in the pump having never pulled one but if the shaft seal fails, coolant can enter into the engine that way. Another way to check for coolant is to pressurize the rad and check for internal leaks assuming nothing is evident externally. Pull the sump, clean and dry the inside of the engine with a solvent and apply pressure to the rad. Leave the rad/engine pressurized for a period of time looking for any slight leaks at the sleeves, or the water pump area. I'd do this before pulling the head. A blown head gasket should cause the rad to become overpressurized and might discolour the coolant. If this isn't happening, then you usually have a pinched seal or torn gasket between an oil and coolant port in the head to cylinder block area.
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