AutoRX would be a great way to clean it out for synthetic, but I would avoid using a solvent flush like the over the counter stuff and Amsoil's flush. The solvent flush may break loose some big chunks of sludge and lodge them in an oil galley. A solvent flush would be ok in a car with 30K miles or so, but in a car with 116K run on dino, I would stay away. Go for the gentle, methodical cleaning of the AutoRX. Much safer. I've used it in a high mileage, negelected car and low mileage maintained truck, both with good results.