You could try U.K. book stores. I found a english version of a haynes manual for the 280m110 w123 that is not available in the U.S.
edit; found it as pdf here. http://crazyaboutmercedes.com/en/mercedes-benz-engine-manuals/4-mercedes-benz-service-manual-engines-m-115.html

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Chris
84 280sl
82 300d euro