My recollection is that Mercedes specifies a specific standard for their ATF, and the ones spec'd for the newer transmissions typically covers the older ones too. That said, the ones in the official Mercedes bottles is the same as Shell ATF. In fact, the last time I bought some from the dealer, they gave me Shell branded stuff.
I use Fuchs Titan ATF 3353 Dexron III buying the stuff in 20lt drums like for Mobil1 for the M113 engine About Fuchs TITAN ATF 3353 Automatic Transmission Fluid
Multifunctional DEXRON III Generation ATF for automatic transmissions as well as any other ATF-applications. Developed for the latest generation of Mercedes-Benz 7-speed automatic transmissions (NAG 2), applicable as well for the preceding 5-speed automatic transmissions (NAG 1). Offers fuel-efficiency potential.
TITAN ATF 3353 has been developed to satisfy highest demands to shifting comfort in modern automatic transmissions by Mercedes-Benz. TITAN ATF 3353 is formulated with selected high quality base oils in combination with a specially developed, unique additive technology. Demanding quality control ensures constant product performance.
TITAN ATF 3353 is specially recommended for the latest generation of Mercedes Benz 7-speed automatic gearboxes (NAG 2), as well as for all former 5-speed transmissions (NAG 1). TITAN ATF 3353 can also be used in many applications where DEXRON III-type fluids are recommended.