We looked (not for long) at Merc's W215 CL500 a few years ago to replace the now 20 year old W124 coupe we still have.

Didn't look for long, found a 3 year old CL500 we liked the look of, aluminium panels over a steel frame, rear wheelarch a chunk roughly 6" long had corroded completely away and i mean vanished and continuing to crumble away, and on both rear quarter panels presumably where the steel frame inside touches there was signficant bubbling of the paint from deep inside...sales bod seemed amazed that i'd spotted that in 30 seconds and we were walking away some 30 seconds later, never bothered to lift the bonnet or boot though maybe that might have been worth it just to poke fun at this piece of quality German engineering when i found more disasters in their infancy.

Our lorry tanker trailers are aluminium ladder chassis, what they gain in weight saving i'm not at all sure is cost effective, they suffer with terrible salt corrosion and gain expensive cracks in quite short order.

The pressure tanks themselves are aluminium but very well painted and being high up don't suffer with salt ingress anywhere near.

I'll stick with properly painted all steel cars thanks all the same, hopefully with some decent wax injection by the maker when new.

The "all-aluminium" cars have plenty of steel components bolted to them.

Yes they do and one example I can think of because I recently researched it is the serious corrosion caused by steel front lower wishbone mount shims(steel) to the chassis (aluminium) on a lotus elise/

Out in the countryside in north-west France where I am it is quite common to see a lot of old French cars and vans still going as daily drives , not just as classics, Renault 4's and the odd early Renault 3-early Mk1 Renault 5's mostly because there is no annual road tax in france, but there is a registration tax on change of ownership so the older locals avoid changing their cars.

The rural French don't do "keeping up with the Joneses" with their cars, so if it keeps going they keep it - the annual expense is just fuel, maintenance and minimum legal insurance with the mot every two years, so it's cheap motoring.