he 87 300D is a 3.0 6 cylinder and mine is a 2.5 5 cylinder. I think the extra copper washer in yours amy be for a different application, although it seems strange for the washer to be where you state it is. Generally copper washers are used to seal two metal surfaces. The center shafter in the filter assembly is sealed with the rubber washer that is bulit into the new oil filter, at leat on the 2.5 diesel.