That is a handy guide, isn't it, Mr. Sherman? And a recent one, too. That, too, is a plus.
It was written by the FTC for businessmen (and women, of course) to assist them in complying with the statute. Which is really interesting when you stop and think about it, because one of the original purposes of the Magnuson Moss Act, perhaps the paramount one, was to protect consumers from arbitrary denials of warranty coverage by manufacturers. So, in a sense, we are coming full circle.
What I mean by that is many consumers have become much more sophisticated in their understanding of their rights under the law than businessmen and managers. But, as you point out (not to put words in your mouth), Magnuson Moss is not a blank check to (mixing metaphors) run rough-shod over maintenance requirements and then come around seeking warranty coverage.
But I'm not saying that. We are discussing using a 5W-30 weight synthetic oil in place of a conventional 5W-20 weight oil to protect an engine against extremes of heat and oil shearing in the middle of the summer. And it was for those very purposes that M1 5W-30 was certified by Honda and Exxon-Mobil to meet high engine-oil temperature (HTO-06) requirements set by Honda. They can't very well now argue that the product they certified is unfit for its intended use, now can they? And that's a key legal concept in this instance: vis -- is the substitute oil fit for its intended use. Clearly it is. We win.
Furthermore, I agree with you that it would be very difficult for a consumer who (quoting you) "ran 20W-50 in the middle of an Alaska winter and damaged the VTEC solenoid" to argue successfully that he or she was entitled to the warranty protection of Magnuson Moss. I agree. I didn't suggest otherwise. In your example, the oil weight would be unfit for use in the circumstances you described. Mine isn't. We win.
But, you raise an interesting point: Just who has the burden of proof in the example you chose, or for that matter, in any instance in which the consumer seeks warranty coverage?
It's the manufacturer, Mr. Sherman. Always. Never the consumer. The burden is always on the manufacturer under Magnuson Moss to prove -- prove, not just argue or suggest or infer, but prove -- that the item or product the consumer used caused the damage which resulted in the claim.
So, in the case of the OP, for Honda to win the right to deny warranty coverage for (in the extreme case) an engine failure (or any other mechanical failure), Honda would have to prove -- i.e., introduce in court actual physical evidence (the broken parts) supported by expert testimony -- to establish as a matter of law that it was Mobil 1 5W-30 synthetic oil that caused the damage which the consumer asserts is covered by the manufacturer's warranty. D*mn high burden of proof. And in the circumstances we are discussing, Honda can't meet it and would not try. That's Magnuson Moss. And it's why the OP has absolutely nothing to fear and everything to gain in his use of M1 5W-30 oil.
As I said pages ago, we could debate this endlessly. The ultimate resolution is, of course, the courthouse. But, in my experience, there is no way in h*ll either Honda or Exxon-Mobil would deny a warranty claim arising out of the use of M1 5W-30, much less take these facts to trial or arbitration.