I am assuming Mobil 1 EP and Mobil 1 ESP has different formulation?That to my knowledge is the only Castrol retail product that carries MB229.71 approval, whereas the only Mobil oil that has MB-Approval 229.71 is ESP 0W20, Mobil 1 EP is only .8% ash to my knowledge with the mostly PAO composition and that it's been engineered for drain intervals up to 20,000mi, I wonder what really keeps it from being MB229.71 other than Mobil wanting you to fork out more cash for a Euro specific oil.
The Castrol EP is also 20k miles OCI.