I think there was some manufacturing plant re-shuffling in europe, and what used to be German Castrol, is now Belgian Castrol. Both are mostly PAO based as I recall, because of stricter euro labeling requirements. I do not remember the exact details, but recall something like to be labelled fully synthetic in Europe (or Germany, I forget) it cannot be made of group 3. Someone please correct me if have better info.
As far as I know, it is not possible to source German Castrol any more, because the new stock is made in Belgium now. So if you catch a bottle that says German made, it must be NOS. The 0w40 m1 is a good oil, mostly GTL based, with some PAO.