The transmission shop I worked in for 5 months put Dexron 3 in Mercedes, just like everything else. It was a premium shop, good reputation in town. Neither of the mercedes I r&r'd had burned fluid, just trash from worn clutches& bands. You can smell burned fluid, it's stinko. If a car doesn't burn the Fluid (modern GM's do), and the car hasn't been driven through high water, I not sure why to change the fluid ever, except 3 months before you rebuild the transmission because the clutches are worn out. Most burned fluid (not GM) is caused by worn out clutches and slipping.