I can't recall what manual trans oil I used, too long ago. My bet is whatever weight oil the manual called for.
It came up because I was considering buying it (the 79 240D) and a tech said that he'd driven it and that it snicked 2nd gear, that someone probably put ATF in the box.
I was a bit amazed. Right then and there he pulled it on his lift, changed the the trans oil and it shifted perfectly for over 150k miles.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)