Any machine, if it is looked after, and not abused will last for ages. A friend is still using, as far as I know, a Drummond dating from the early 1900s. I know of several Myford M types that are still being used by happy owners.
Those machines must be 70+ years old. The ML7 was launched in 1947 so there must be many that are 70 years old and still functioning satisfactorily.
I started with a ML7, without a clutch, but bore in mind the comments about electric motors not liking the heating effect of the current inrush of frequent start ups. My lathe had at least one previous owner, judged by the wood dust around it. The motor never showed signs of damage from the number of starts that I gave it.
It was replaced after several years with a Chinese 12 x 24 lathe, to have a larger Mandrel bore than 2 MT.
After over 16 years that seems to be as good as new, apart from the cosmetic aspects. There have been a very few small problems; but nothing that could not be cured quite easily and quickly.
Remember the adage about Good Tunes being played on old fiddles!
Misuse can ruin a new machine in as little as minutes. Care, and use within limitations, can keep a machine working accurately for many years.
If you think about buying any used machinery, ensure that all the functions work, and that it is not worn or damaged, and all the accessories that should be there, are. CAVEAT EMPTOR!
Howard