"Even if there is zero corrosion, engines have a lot of soft parts,
rubber and cork gaskets and the like that go bad with age alone."

Then why doesn't mine leak? or use oil? or show some iron in the oil
analysis (we'll have an update on that in a couple of months though).

I agree there are a lot of raunchy abused and marginally overhauled
engines out there, but with proper care some engines can last well
beyond TBO.

Even aircraft engines don't use cork anymore.