I found this site, seems to have hundreds of articles for repairing/checking the OM617 engine. All articles written in English, with great pictures (seems to be from a shop manual or something), the rest of the site is in Polish but I think you'll manage to navigate your way around..

http://mb.auto.pl/component/option,com_alphacontent/section,10/Itemid,64/

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Tomas, Sweden
1966 Mercedes Benz 230S with OM617.912, automatic. Disk brakes from W108
1983 Mercedes Benz 300TD grey, OM617.912 and 5-speed manual
1983 Mercedes Benz 300TD blue 7-seater, OM617.912 and 5-speed manual