I went to my dealer for a LOF change and I requested Full Synthetic (FS) Dexos be used. I assumed FS would be best for wear & tear as well as better mpg. The Service Manager strongly suggested to go with the Blend Dexos, claiming that GM recommends the Blend, that Blend is just as good as the FS. Also claimed that while FS would NOT void the warranty, it would just be a waste of money. I have to assume that if the dealers objective was to just increase revenue they would have gladly just used FS and charged me more. I've seen many past opinions on this subject but has anyone seen anything more lately from GM, other than the manual recommending Dexos is recommended?