i have a running 80s vehicle with over 400k kilometers (its a VW T3)

Survivorship bias. Try doing that with an Austin Metro, Citroen Visa, Fiat Strada.

On average modern cars are significantly better than what we had in the 80s

I had one too!

Mine had a Subaru engine, Mercedes wheels, Audi Drive train, a Porsche suspension, and brakes from a Toyota Highlander.

How did you keep your Volkswagen running?