oil in water

[RobB]

Hi I have recently been getting oil in the water of my 93 mk2 espace. I removed the head as shortly before this had happened the car had overheated , due to a split heater hose and I thought it must be a blown gasket. The gasket looks fine though. I still cant think of any other  way for oil to get in the coolant forming a frothy mess unless maybe a fine crack in the head. The head looks fine. Would it be reasonable to assume that the leak in the gasket could be too slight to notice.
Rob