After reading several threads I've come to the conclusion that there is no consensus on general oil viscosity to use. The manual says, 0w40 the inside of the hood says 0w30, Troy Jeup (a S63TU rebulder) recommends 5w50 redline discussed extensively here https://f10.m5post.com/forums/sh...
The thicker the oil is at this temp, the higher its rating will be. Thus, 0W30 motor oil would be less resistant to high temperatures than 0W40 oil, for example. 0W30 would become watery at lower temperatures than 0W40 motor oil, while the latter would be able to stay viscous enough ...