I found a full case of old unused oil at my dad's house a few weeks ago, don't know the age of it but it could easily be well over 10 years. I put it in my 5.3 and am keeping a close eye on it. So far, so good. One of the factors to consider might be that today's oils are superior to the older stuff, but I figure that if it worked fine then, it should still be okay.
