Your link didn't work for me... but yes the rubber O ring.. be sure to use proper torque on the throttle body..

http://www.ebay.com/itm/Mercedes-Benz-W202-W203-W204-NEW-GENUINE-Throttle-Housing-O-Ring-305-997-03-45-/151161574603?pt=Motors_Car_Truck_Parts_Accessories&hash=item2331ee94cb&vxp=mtr