I have never seen them list the approved fluids on the web, but they (MBUSA) do have a booklet that is available free-of-charge (except for shipping charge) that you can get if you call 1-800-Ask-Mercedes. Its title is "Factory Approved Service Products" and its tech info order number is S-0473-00M.
There are no synthetic ATF fluids on the list that I can tell. JRBrown's list looks pretty current with the addition of MB ATF, part number 001 989 21 03 10. Hope this helps.
[This message has been edited by dakota (edited 10-15-2000).]