My stepdad went to get his Power Wagon serviced today. His rear diff cover has some rust on it, which is causing the paint to peel off. Now he says that the dealership won't replace that under warranty because they don't cover rust. But the argument is that the Service person states that the diff cover is made out of aluminum and that some aluminum rusts. My stepdad argued that point saying that aluminum doesn't rust just look at the aluminum hull boats. The service guy then went on to add that yes aluminum does rust, to prove it look at the exhaust tip and you would see some rust. So the service guy was saying that the rear diff cover is made out of aluminum and so is the exhaust. Can I get some truth behind this as to what the AAM axle diff cover and exhaust is made out of?