I wanna change the fluid in the Manual trans in the 240D. I have been looking at other threads and their seems to be two distinct opinions when it comes to this subject.

On opinion is use Transmission fluid as that is what Mercedes reccomends

Another opinion is to use Redline MTL as it is designed for Manual transmissions and is thicker and more suited to lubing these transmissions but some people claim they harm syncronizers. People who use redline also say that mercedes recommended atf and atf today is different than the atf sold 20-30 years ago (which I can understand)

So I'm looking for some of you guys to chime in that drive four or five speeds to set me straight because I dont know what to put in it.
Keep in mind my car is a 1979 240d And shifts good but it is a new purchase and I dont know the age or condition of the old fluid so I want to change it.

Thanks in advance...