I'm going for the same project in the near future. I'm going to try vinigar and water solution. Just like cleaning water spots from windows. Vinigar will deaden rust and desolve calcium.

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1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)