tried Rotella T6 in my BMW years back wound up failing smog with it . Changed it out to an excellent Quaker State full synthetic and passed no problem. M3’s tend to be oil burners by nature it’s known fact among owners.
Moral of the story is T6 was originally designed for diesels and burns dirty while providing only ok protraction.It was big in the BMW world for a minute I believe it’s heavy in Zinc. . I would not run it ever again.
The Quaker state is under the radar but high rated shear / stress and breakdown tested by a master engine builder. Who actually published his info on the net which has been linked to off this site before.