No, I don't have a 126 or a 190. I have an 88 124, 300E with a manual transmission. This is a US car. There were about 700 300E 5 speeds brought to the US by MBUSA in the 1986 model year and 300 more in the 1988 model year.

One of my 240D's, I don't remember which specified 10W30 motor oil for the transmission. I think it was my 77, but I'm not sure. My 84 Euro 240D still has the original transmission and has never been opened, still in great shape. It has 533,000 miles and has had 10W30 motor oil since about the 100,000 mile mark. My 300E has had 10W30 motor oil since about the 80,000 mile mark and the trans is still perfect.

Dexron will lubricate a manual transmission just fine. The only problem with it is that since the eighties ATF has changed in formula such that it will attack many of the seal materials of the eighties. This shows up more often in the power steering systems of the eighties.

The much newer cars will work okay with ATF because they have seal material that was developed/selected with this fluid in mind.

Have a great day,