From my experiences, if something is really important enough to me, I do not ask the question that may get an answer I do not want on the phone. I got in person (when at all possible) and have a face to face conversation.
In this example I would have gone to the dealer to buy the part. Before going to the parts counter I would have talked to whom ever I though had more control over the business and mentioned the problem with the cable. I'd get that person's "feel" for the problem....if it's a common one, or rare. Only then, if it was a common problem would I even pursue them giving a free replacement part. And if it was a common problem, I'd ask how they typically handled it. I would then expect to have my problem handled just as they did others. If it's not a typical component problem, I'd go over to the parts counter and get it and be done with it.
I grew up with a hard working work ethic and not expecting others to help me with my chores or obligations. The same for situations like this.
The reasons we have contracts, leases, loans, etc that are signed by both parties is to eliminate mis-understandings later on. The signed agreement has a beninning and ending date. To expect the business owner to extend the date (because it generates more business by my positive feedback in the example given in this thread) demonstrates the difference found in our society, especially these days!
I can read this thread and almost determine the political party by what is expressed.