Don't judge every facility guilty just because You happened to be let down by one!
That said if You do have a legitimate complaint You should be taking every step possible to bring that to the attention of the Senior Management of the Establishment in question!
If it is a Genuine Cummins Shop there must be a Manager of Corporate relations that You can contact with the documented details of Your Complaint!
I have always found that regardless of the situation most companies have someone with whom to discuss the problem and are willing to resolve any issues to the satisfaction of all concerned.