I went through this exercise 25 years and 25,000 miles ago for my '88 190E 2.6 special order five-speed. IIRC the Mercedes spec is 20W-20 non-detergent engine oil (try finding that, today) or Type A Suffix A ATF that is the old, original GM ATF spec going back the first Hydramatics in the 1940s that had a small amount of whale oil as a friction modifier to prevent wet clutch chatter.

Of course, whale oil was outlawed in the 1970s, and the current anti-chatter additive is a synthetic product.

After more research I decided to go with Redline MTL, which is the same viscosity range as ATF (70W-75), but is formulated for manual transmissions that are speced for ATF, so it probably doesn't have the friction modifier, which is not necessary for synchromesh transmissions, but I think it's okay to use modern Dexron.

You'll find a similar situation for the rear axle oil. The Mercedes spec is 85W-90 GL-5. I did ascertain that Pennzoil offered this product, but couldn't find it... finally called Pennzoil and they said it's not available in North America, so I used commonly available 80W-90 GL-5.

I was chagrined that Mercedes recommended lubricant products than are either long obsolete or not available in the USA.

Duke