My guzzi - an air cooled twin, but I do realise Norton owners have additional problems - has used Mobil1 since I could first get it (only at ESSO stations back then). Motor has now done 160,000+ miles, and still does everything necessary.
The first thing I noticed when I first started using it was how much cooler the engine felt and how much smoother and happier it was running in high temps in the south of France, Typically 40+C.
A totally un neccessary stripdown (to adjust the squish on the Le Mans heads) showed everything OK and other than seals and gaskets, nothing was replaced. Cams and followers - often a point of wear in guzzi's were fine.
It was explained to me by an industry insider, that here in the UK at least, the crude from a well belonging to company A, goes to the nearest refinery, not transported extra miles to company A's refinery.
The output is then supplied to various purchasers who could be any of the other oil companies or oil packers/marketeers. It is then up to them to devise an additive package, supplied by one of the very small number of companies world wide who specialise in that sort of thing.
The wells and platforms, refineries, blending and packing plants may fly a particular company flag, but the product in the shop is just as likely to be a composite of many hands.
This is what I was told happens here, and it was a while ago, maybe in other countries laws on anti monopoly or the presence of a state monopoly may distort the free market model.
The point being that Castrol* are not producers in the find, extract and refine sense, but in the tricky and crucial bit of selecting and blending base stocks and devising/specifying additive packages they are.
*also Fuchs/Silkolene, Morris's and many other brands which adorn shelves in car and bike shops.
