What you're describing sounds an awful lot like a warped head. Oil in the coolant, overheating (which only makes the warpage worse). Wet carpet and the smell of coolant inside the car can be caused by a leaking heater core. The oil level may be staying up due to coolant leaking in or fuel bypassing the rings and ending up in the crankcase. There's also a problem with the PCV system that can happen occasionally. Ask any BMW tech about the "hooter valve" next time you're at the dealer. I'd have it in for a compression test and a scan asap.