Hi Ken,
Look at the last 7 Alpha-numerical of your car VIN. For E class with VIN up to A379346, it uses 2 retaining pins, for VIN A379347 and later, it uses one retaining pin. My E430 is 2000 and the last 7 VIN is B104087, so that it needs 1 Retaning pin.
Hope this will help you buy the correct rear pad.
Have a nice day.