I downloaded and reviewed the oil analysis document. I was interested in the results of conventional Castrol GTX oil because that's what i've used (now at 64k miles) and from the results of that study it looks like i can get away with changing oil and filter at 5k miles instead of the 4k interval i've been using. In the study, the Castrol GTX was described as 5w30 in one place, but 10w30 in another: which one is it?