My question would be do the limited and base have an oil cooler like the SRT6? If so, it could be the oil cooler or just the two little gaskets it has. You can remove the oil cooler and bench test it with air and a bucket of water (see YouTube). If you see air bubbles replace the oil cooler and gaskets. If no air bubbles just replace the gaskets. Hopefully it is just nothing but if oil is in the coolant that is symptom of the oil cooler or oil cooler gaskets being bad.