gsxr,

The reason MB specifies ATF for their manual transmissions is mainly due to the fact that the Fatherland is a significantly colder climate than most places. ATF was considered better than typical gear oils of the old days because it flowed at these low temperatures and gear lubricants didn't.

Consequently it is tough shifting a transmission for the first few minutes or more when you start up at near zero degrees F with transmission full of gear lubricant. ATF seemed to address this issue adequately and did not result in rapid damage to other aspects of the transmission in the hands of a rational operator. Like cabbies in the Fatherland, who performed maintenance on their cars religiously and limited the number of quick starts and racing shifts to preserve their profit margins. In those days the cab driver was also the cab owner. May still be that way over there.

Redline's MTL has about the same viscosity as ATF's at low temperatures where it is important to improve performance, and they offer added protection of extreme pressure additives for gear contact surface wear reduction, as well as friction modifiers to make the synchros perform better with less stress and wear.

Given the synchros are the weakest link in nearly every synchromesh transmission, it is not unreasonable to seek a product that addresses this issue now that it is available. Until recently this additive was not available for any ATF, however, Redline has recently begun to offer an ATF product that also contains this friction modifier (D4 ATF). It is, like MTL, a synthetic GL-4 gear oil, with fewer of the extreme pressure protection additives and viscosity modifiers (for higher temperatures). D4 ATF is also recommended by Redline for manual transmissions that manufacturer's recommend ATF be used in if the extreme pressure additive package is not necessary.

Since I live in a place now that is far less frigid than the Fatherland in Winter, and far warmer in Summer, I have opted for the MTL product. I have been using it in my cars for pretty close to 15 years. I have yet to ruin a transmission and only have one more kid to get through the learning to drive a manual stage. Believe me, the 1982 240D 4-speed has done a few tricks at my daughter's hand that (and foot) I have never considered possible before, and my son is very busy stressing out the 1986 190E 2.3-16 5-speed on a regular basis. So I consider the extreme pressure additives necessary.

The point is, not only have the ATF products improved over time, so have the other options, and now the choice of ATF vs. Synthetic ATF vs. Synthetic GL-4 gear lubricant vs. dino GL-4 vs 10W30 engine oils is more of a multi-dimensional decision than it was in the late 1970's. The choices today can be between technically sound alternates and based on how each fits your operating envelop (environment and driving style).

Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)