This is going to sound patronizing, but isn't intended that way. I would suggest you try a library. Or more specifically, talk to a librarian. They are an incredible resource of information and may be able to lead you in the right direction. Perhaps they even have the book available for checkout.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).