Wash your ml350 weekly, more frequently if the paint has been exposed to harsh(clear coat damaged) conditions like salty roads or dust. Washing keeps contaminants off the clear coat, which will protect it from breaking down. Use soft, gentle soaps, brushes and cloths to avoid scratches.
Avoid holding high-pressure water sprayers near your vehicle. The spray can damage the clear coat, which can eventually make it peel away.
Wax your vehicle at least every three months. Use soft cloths or sponges to apply a good-quality vehicle wax. Follow manufacturer's directions.