I guess the key here is how long youhave owned the car and how you have maintained it. Since you are checking fluids, this is a good sign, but have you loaned it out or possibly had inexperienced people work on it? Is the transmission leaking? Since there is the wrong fluid in the radiator, it should be addressed, and a leak check is in order anyway for the odor in with the heat on. A little patience and trouble shooting may avoid replacing the radiator! But something must be going on either with the transission, radiator, or heater core, or ??? Adding fluid to either of these systems on a regular basis is not good. Stay after it and you will find the answer!