Remember this :
Castrol (and all the others) does NOT exist to supply you with good oil.
Castrol exists ONLY to make as much profit as possible for the people who own the Castrol Oil company.
The question then becomes HOW can Castrol make as much profit as possible?
The answer is simple - spend as little as possible making the product, and charge as much as possible for selling it.
So who PAYS for Castrol's profits?
Not me anyway, because I use Tractor Universal in ALL my engines.
My TD5 Disco is over 90,000 miles on it, runs like a sweetie, and the insides of the engine are the cleanest I think I have ever seen in an engine with some miles on it.
CharlesY