The 240D clutch and transmission are easy and smooth in all temperature.
I've never had an owners manual for my Euro 240D. I think I read in the manual for my US '77 240D that I had prior to the Euro that it was motor oil in the transmission. As MBDoc says, if you use ATF, use TYPE A. You can still find it. Modern ATF(Mercon) additive packages have changed drastically since your car was built. It may not be good for the seals.