I recently went to a lockshop in Nashville for this reason.(West End lock co.) They can do two types of key ($25 or $3) The 81 and 84 123 cars were the $3 key. The blank that they used was the "Ilco" X82 . It also says on it "MB41" and"For Mercedes". I also have a "Taylor" key that is an X82. These blanks have no plastic on them.
I could not find a place in my locality that could do a properly working key.

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Diesel-guy