I know there are major differences between diesel and gas. However, the 500E with over 100K miles has a cleaner engine/valvetrain than virtually any other MB engine with 35K miles on it that has had the usual 7500 mile services. I forget the exact sump capacity but I think it is around 8-9 quarts. It has had the normal MB service schedule with religious "in-between" changes using conventional 15w40 Quaker State. I know the twin-plug ignition engines are more effecient, cleaner burning, etc so perhaps they will age differently. I have seen how oil changes affect the DOHC engines. Also, the silicon crystal cylider liners are nothing new. They were used in the M119 V8's and the V12 starting in 92 model year. But it does lessen friction, reduce heat, and is more durable than the most metals. Your engine may be their debut in a diesel though. Considering the cost of engine repairs oil may be the cheapest insurance available.