Oil in coolant

You did not list any details about your car. If it has an automatic transmission, there is a fluid cooler that is usually built into the radiator. If that tube corrodes through, transmission fluid will mix with the coolant. Transmission fluid will rot heater and radiator hoses fro the inside. Antifreeze in the transmission will melt the soft outer layer of some of the bushings. Both fluids should be flushed if the transmission cooler is leaking in the radiator.