Oil in the water

I checked and clean my van this afternoon. I performed tightening on different parts of the vehicle for its quarterly maintenance. As I opened the radiator cap, I found out that there is an oil inside the radiator reservoir. I already conclude that its cylinder head gasket is worn out already for there is oil in water. The oil hole in the in the engine is the only passage from the outside parts of oil galleries and there is also water holes inside the block and if the gasket is worn out, there is a possibility that oil will leak into its water galleries between the cylinder head gasket and its block. I will bring this van to the Mercedes Benz repair shop to replace the cylinder head gasket this coming Monday next week.