And we are talking about classics from the eighties. Cars with automatic gearboxes but also cars with power steering. The editorial Audi from 1983 was maintained by the previous owner. He had overhauled his power steering system and filled it with ATF.
And that went wrong. All seals started to leak ...
Increasingly, for lubricating power steering units and for coolants, part numbers are specified instead of 'ATF'.
It is not uncommon in passenger cars as transmission oils for gearboxes and swingarms last a very long time. This concerns special products that are precisely tailored to the technical requirements and wishes of the transmission manufacturer.
Simply filling with ATF, which went well for decades, becomes a source of trouble. the tank will switch differently, the noise production will change (and the service life will be shortened).
That story is actually comparable to the two different hydraulic fluids that Citroen used. They didn't go together either ...
That is why the car manufacturers supply the lubricant as a 'part'.
The advice is therefore: only use the specified greases, liquids and lubricants.