Engine break in oil?

Group III is Castrol and clones
IMHO the eurospec 0W- 40 BMW LL and MB 229 spec made from natural gas oil is as good as you can get- there are also other grades - the additive package is also synthetic whereas most other oils the additive oil is dino based- which dilutes
III also part of the cost effective blend for +4 trans fluid
what trans +4 has is a controlled and effective additive package and strict licensing from Ma Mopar- something that Dexron III no longer has
the best more modern trans fluid is Citgo Quatrosyn
where it's better is either very cold start ups or very hot usage and it holds up much longer (it's thinner when cold to flow better)
If you are going to change frequently and not hot or cold then +4 works great