You should focus on replacing ALL of the fluids before you start eating through petro products with an engine cleaner. Brakes, radiator, transmission, gas filter(if your model has one) Focus on that first. It'll give you a baseline for the car, and you'll insure its longevity.
After that read the error codes with a stomp test. Then fix whatever comes up. Then you can chip it since you know your transmission and radiator aren't trying to pump cow pies through a tube while you're flooring it. Good luck.