Any Mobil 1 15w-50 red cap or Delvac 1 5w-40 yellow cap is fine. The dealer/po tried 0w-40 in my friends E300D in the winter I don't know if it made a difference.

Now as to the trans fluid techs seem to be devided on it. Some say filled for life means just that, while others say every 100k it should be changed. Do a search and come to your on conclusions. However you cannot change it yourself. The dealer can plug the car in to determine the fluid temp, their is a sensor in their somewhere. It has to be exactly 80c to get a proper reading. This is a dealer only job.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200