What upgrade could do that with ICE vehicles? Switching to unleaded or low-sulphur diesel were about the only things, everything further improvement (catalytic converters, better efficiency) requires changing vehicles each time.
Unleaded required car changes, too.
Earlier vehicles had valve stems in the engine - especially on the exhaust valve - which were lubricated by lead from the antiknock additive. I understand that valve slides had been changed far in advance of the requirement. But the lead additive was sold for a time for owners of older cars to add in order to protect their engines.
Similarly, some antismog oxygenates caused a lot of car fires in older cars, by rotting the rubber tubes in the parts of the fuel systems that had to flex. (This, of course, got a lot of older, high-pollution cars off the roads, reducing pollution (if you don't count the smoke of the burning car...). Thus the environmentalists didn't complain - or warn people.)
Similarly, ethanol stripped the coatings off the inside of older cars' fuel systems and attracted water, starting corrosion; dissolved some gasket sealents, creating manifold leaks, and dissolved plastic float valves from carburators, again causing major damage to (and retirement of) some older cars. (Sometimes some gasoline would have methanol in it, due to a mistake or a crooked supplier, and this would strip things almost immediately.) Many modern vehicles have different materials,and are rated for substantial percentages of ethanol in the gasoline.