Good point, I think youre right!
Theres a chance the oil spec confusion (this is speculation) is what has led to engines such as yours and others getting a rattly top-end, if the '5's have been used for an elongated timeframe. Volvo may well have changed tolerances and materials in euro 4 and beyond to tolerate/make use of a5/b5, which of course the euro 3 doesn't have. Once the damage is done theres no going back without renewal of engine components, but using a different oil can help prevent further degradation and maximise protection, keeping the status quo.
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