If the problem would have been diagnosed properly rather than guessing about the problem, there would be not issue. However, many people in positions of responsibility operate in this manner. And it creates many problems.
Just be thankful you got the second opinion, AND the Cummins dealer refunded your money.
NOW the lesson to be taken away from this is to ALWAYS get a second or maybe even a third opinion - especially when it comes to health care. Physicians are only human and can make honest (and sometimes maybe not honest) mistakes. It always helps to have another pair of eyes look at the problem!!
BE THANKFUL THE ISSUE IS RESOLVED, and without overpaying!!!