1991 Acura Legend oil in my coolant over flow reservoir

I just bought my 1991 Acura Legend, it runs terrific with a 3.2 liter v-6. But i discovered some oil in my coolant over flow reservoir and you can smelll antifreeze when the motor is running.The coolant in the radiator looks fine and the level remains good.I have never found antifreeze on the motor or on the ground, nor has it overheated that I'm aware of. It does NOT overheat, engine remains at just below the half way point on the temperature indicator. No white smoke from the exhaust. The engine runs strong with NO hesitation or sputter. It has had the radiator replaced, but i don't know the history there. Overall the motor is in great shape with recent signs of service (new belts, wires, etc).