I'll second that. For a 722.6 transmission only, I would STRONGLY recommend only using the factory Mercedes fluid. Order it from
Duval if your local dealer's price is too high. I think Phil at MercedesShop can also order it at a decent price. The 722.6 did
not specify a Dexron fluid. Only the older transmissions use Dexron fluid (722.1, .2, .3, .4, .5).
For the rear end, I have used Red Line and Mobil-1 gear oil. However in higher-mileage diffs (approx 200k or more), I have had gear whine develop within 20kmi after the switch, on two different 124's. Could be a fluke, but in the future, I'm sticking with the dino fluid. For limited-slip or ASD Mercdedes diffs, I'd use the factory limited-slip gear lube only (photo is
here). I change the rear gear oil about the same time as the trans fluid (25-30kmi).
I've had problems with non-MB power steering fluid too... so yes, laugh if you want, but I use MB PSF as well. It's about $7/liter but I change it maybe every 5 years or so. I think I can afford that. I also like that the factory stuff is light tan/gold colored, so you can tell if it gets dirty. With red ATF in the PS system, you can't tell anything. Don't forget to change the PS filter, too...
