Well I have no experience with flushing the cooling system with citric acid. But I can tell you this--
Citric acid is a much weaker acid than hydrochloric acid( Muratic acid) or sulfuric acid or nitric acid. The last 3 acids are very corrosive and will corrode most of the metals. Therefore these acids are not recommended to be used in flushing the cooling system.
Citric acid is a milder acid but is acidic enough -when dissolved as per Benz reccomendations- to make the salt deposits dissolve without causing harm to the metal surface of engine, radiator or even gaskets.
Based on these arguments, I think it should work in flushing any cooling system. Most of the commercially available fhushing agents like Prestone etc. are alkaline agents and can dissolve only certain kind of gunk. I am told that the acidic reagent works better than alkaline.

Make your own conclusions but if citric acid can be used on a Benz why not on anyother D- engines.

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles