My 2002 Sienna has nearly 204k miles on it and I got it 70k miles ago in 2012. Ever since I've been running Castrol's GTX High Mileage synthetic blend in it. I use premium filters and try to shoot for oil changes around 5000 miles or a bit less. I just got my most recent oil analysis back from Blackstone (pictured) and the numbers are all pretty good. Sooo... I'm wondering if at this late date and after all this time there's any real benefit to me and switching to a high mileage FULL synthetic? The benefits I think there would be, or I would be looking for, would be those generally associated with engines and full synthetic oil as well as extending my OCIs a couple thousand miles. But I'm also wondering if after all this time that.... well, I really don't know any other better way to say it, so I'll just say it in a way that probably sounds a little ignorant... maybe the internal parts of my engine are held together by 204,000 miles of conventional or blended oil gunk and full synthetic oil might clean that all out and cause problems. Thoughts?