If you don't have "access" to the areas where the work is being done,
then you don't know what is being done - period - so, you really don't
know anything...
And being that the majority of the population of the USA lives along
the coasts, therefore the majority of oil coolers flying are exposed to
salt air... Not all of them have to fall into the ocean and sink 3000
feet, so failed oil coolers would have wound up on land and been
exposed to FSDO and NTSB investigators...
And the coating of the coolers is visible to the eye...
And one would think that the mechanic who has to sign off the 100 hour
and the annual inspections would see the corrosion long before it eats
a hole through the tubes...
While it is possible that the manufacturer is making false
certifications it is not probable, so why should we believe you?

Denny