My brother has a 98 Wrangler with the 6 cyl. When he changed his oil yesterday, I was poking around under the hood and noticed that the overflow container for the rad looked dirty. I opened it up and found it to contain a nasty mixture of oil and coolant. I opened up the rad cap and the coolant looked green and showed no signs of having oil on it. The exhaust smells fine and does not smoke at all. It has no perfromace loss and shows no signs of overheating or cooling issues whatsoever. So what does this mean? Minor leak at head gasket I'm thinking?