I drive a 97 turbo wagon here in Norway where they salt the living bejeezus out of the roads. I know Volvo gives an eight-year warranty on rust protection, which is about up on mine. What kind of a rust preventive treatment should I be looking at (standard asphalt undercoating on top of what's there?), and when should I start thinking about having it done? I take excellent care of this vehicle and clean it top and underneath when I've been driving on salted roads. Still, I know the salt is eventually going to get to it. Advice, please. Dick