[Al Skierkiewicz]

Ed,
Too late to check now, but the breaker does have a failure mode that that prevents high current flow but appears normal otherwise. As a test, if the red button is tapped lightly and the breaker opens or becomes intermittent, the internal contacts are out of alignment.
There are also issues if the mounting/frame should flex, small cracks in the case develop. I have seen cracks pull the internals out of alignment.

Do you still have the breaker?