Maybe recommend for the owner to get an oil analysis? If it's that bad, what's wearing in there?

Any history of 'stop-leak' use in the oil system, like "my VC gasket is leaking, I'll put this stuff in here to stop it..."

I'd maybe go the other route from Mobil 1 - use a cheap, high-detergent based oil and change more often. Maybe use an engine flush product?