Are you sure that Quantum is Castrol?
Quantum is not "Castrol" in another branded can. But Quantum are
developed by Castrol. They are made in Belguim at the UK Lubricants plc plant, along with all Castrol, BP, Aral, and Adamol brands. Castrol is now a BP subsidiary. And as further proof Quantum are Castrol developed is their technical phone number and address - being Pipers Way in Swindon. Anyone who knows anything about lubricants will know that Pipers Way has been the head office of Castrol for years - and when you phone up the technical helpline, you actually speak to Castrol engineers.
Another myth is that Quantum LongLife 3 is exactly the same formulation as say the 504/507 specific Castrol Edge 5w30 - it categorically is not. The datasheets prove this, as will a chat with any of the technical helplines. Yes, they'll both pass the VW LL3 spec, but the Quantum brew uses slightly "inferior" constituents (ie, base stocks and additives packages) compared to their official Castrol branded counterparts.
I was told by a VW tech that it is premium oil from the VW approved range but whoever has the cheapest tender gets to put it in the bottle. I.e it could be Castrol one month but Mobil or Fuchs the next?
Another VW employee excelling in the art of utter bullsh*t!
Next time you pass your local TPS, look at the address on all the 208 litre Quantum barrels . . .