About 10 years ago I went through about a dozen warranty claims for internal engine damage on emergency generators, 4 cylinder diesel engines. The manufacturer spent their effort looking at the internal parts of the engine to determine what happened and they never asked what kind of oil or filter or the schedule for maintenance. They told me that they could tell what happened with their inspection, measurements, testing and lab analysis and they were correct on every one. The 2 engines that were abused, that is skipped maintenance were really easy to spot and 3 engines had bearing failures not related to maintenance. Anyway all the determinations were made and the customer was satisfied with the results. I reviewed the photos, the test procedures, the lab work and the reports and they all combined to create a very compelling case for each engine. There were not arguments or disputes on either side and the matters were quickly settled to everyone's satisfaction. There was no drama. One manufacturer's rep said this might not be so easy dealing with automobiles and the general public because some owners are easily distracted.