I think it depends on your car. On the 126, ATF is fine through 1985. From 1986, there's a specific power steering fluid to use. I use a fluid with a Febi label. However, just as my 3 126s came to me with green coolant, they came with red power steering fluid. The only thing I've done to all 3 is change the hose from the power steering cooling loop to the pump reservoir because of leaks. The SD has the only leak and it's minor seeping from the front pump seal. It doesn't seem worth fixing at this point. Of course, I changed all 3 to the Febi stuff.
I don't know what the year breaks are for other MBs.