TSoA,
Life is short - run the 15w-40 and spend your time worrying about more important things like biological weapons and world hunger. You have to keep life in perspective, seriously ....
Oil related failures under warranty are almost unheard of, and a simple $20.00 oil analysis will prove that the oil wasn't at fault ...In fact, oil analysis is often used by the vehicle manufacturer precisely to resolve these situation. I've shipped oil analysis kits to Germany in the past, and the oil samples are air mailed to Oil Analyzers in Wisconsin for testing. So I can assist you if need be....
Tooslick
Dixie Synthetics