I will not use ATF in manual transmissions unless it is specifically called for.
I had a '79 240D that would grind in 2nd gear right after I bought it. I was told the transmission was worn out and it needed a rebuild.
I changed the transmission oil from ATF to the oil (I forgot the weight) that Mercedes called for, and it never had another problem. I drove it for over 85,000 before I sold it.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)