While not a final authority on the topic, I did some research before putting Red Line ATF in my 400e and it has suffered no ill effects. In fact, the car shifts far more smoothly than before One tech said that sometimes synthetic ATF can cause slippage. He added it would only happen if the transmission was more or less ready to do this anyway…
'00 ML320 "Casper"
'92 400E "Stella"