MB switched to the EGR exhaust manifold around mid 1980, so some late production 1980 300SDs won't have the non-EGR exhaust manifold. However, Euro spec 81-85 300TD Turbo wagons and the rare Japan spec 1981-1985 300SDs will have the non-EGR exhaust manifolds.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.