I don't know why I did not become a Castrol motor oil fan. Many people who knew something about motor oils recommended it to me. A guy who used to be the manager of a Nissan dealership and then opened up his own used car dealership recommended Castrol. Two guys involved in motor oil distribution recommended it. A woman mechanic who is very highly regarded recommends it. A woman in the service department of a Saturn dealership (where they were using Quaker State oil) told me she uses it in her Saturn. I kept on using Pennzoil (and sometimes Quaker State) until I heard some negative (and probably false) stuff about Pennzoil and Quaker State.
I nearly became a Castrol guy again when Castrol came out with Castrol Syntec. And then I heard a lot of negative stuff about it.
Now Castrol is selling this German Castrol in the USA. Only problem is that it is fairly hard to find. I think the German Castrol is the real deal. But I have learned not to have any brand loyalty.
Now, some people say that the German Castrol is a Group III, with perhaps a lot of esters in it. I guess that is possible, in order for them to keep the price down. Perhaps the German Castrol is second line compared to some other European motor oils. All I know is, it seems to perform really good in my car.