Just as a datapoint, my SDL was filled with red ATF when I got it. When I flushed it out, I refilled with the "correct" Mercedes PS fluid. After about a month it started leaking profusely. Mainly from the steering box where there were 0 leaks before. I flushed it back out with about a gallon of ATF and refilled the system with fresh Max-Life ATF and it stopped leaking after about a week. Been over a year at this point and not ONE DROP leaked anywhere. If your system already has ATF in it, keep it that way if it isn't leaking.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]