A metal/restoration guy I know stabs the metal with an ice pick to decide what to do... if the pick penetrates the metal then it is a 1-2 year repair if it does not it could be a 5 year + repair in wet climates (he lives in Maryland). I live in Az which is not a fair comparison for 90% of the country. It could last forever if you never get it wet here.
That would probably mean a car that is only driven occasionally and not often in bad conditions may be good for 50 years or more just by rough estimates and if it passed the ice pick test.
What is the cost for getting a repair like that done ?