Mercedes-Benz recommends using ATF for power steering in the 1998 E320. The specific type of ATF required is Mercedes-Benz ATF 134. This fluid is specifically formulated for use in Mercedes-Benz vehicles and meets the manufacturer's specifications for performance and longevity.
Note: Do not use any other type of fluid in the power steering system of your 1998 Mercedes E320, as this could damage the system and cause it to fail.