One tiny piece of info, my 1985 300D CA W123 uses the transmission of later 1986+ 300D's. I found that out when changing the front seal while I had the engine out. I vaguely recall it was a mid-year change, but maybe due to the unique exhaust w/ catalytic converter, in which case might be all 1985 CA. Don't know if 300SD were the same deal, and may not even matter in your problem.