Yeah I would agreed that engine oil all comes from the same place practically. ,
I'm no oil chemsit, but I know they are not all the same! There are many different addictives companies add to their engine oil as well as different API and SAE ratings, and that is what we are paying for. Some addictives prevents rust/corrosion, some allow easier flow under low temperature, and some even prevents foam forming. So if Castrol designed a type of oil for 120,000+ KMs cars, then it must have some special addictives for it. One thing I would not do is cheap out on engine oil, because that is one thing that could break your engine in no time.
Even gasoline, what's the difference between name brand and no-name brand gas besides the price? The addictives!
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