During the two montages of Chalk Air's history, they show a Douglas World Cruiser on floats. The Douglas World Cruisers were military aircraft only, and never used in the civilian market.
Comparing a fatigue failure to bending a paper clip until it beaks is a deeply flawed analogy. Fatigue occurs inside the elastic limit of the metal. It is like using a paper clip on 10 pages a million times, and having the paper clip break. When you bend a paperclip open, you are in the plastic part of the yield curve. After you stop bending, the clip does not go back to its original shape.