I've been through about 4 or 5 tankfuls of ULSD, with no additives added. I've noticed no difference in how the car runs, no drop in fuel mileage, no fuel leaks, but less black smoke, though the "diesely smell" exhaust still lingers.

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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.