I would look carefully for signs of rust problems. There should have been a special inspection/rust proofing service done under warranty for the doors. My 2001 E55 has rust bubbles that formed on the back of the trunk lid by the license plate area in the last year. I also had problems with rust on the back panels below the tail lights that started over 3 years ago. This might have been caused by the AMG bumper rubbing on the metal so I'm not sure if it applies to the E320.