It's very rare you see Mobil 1 thicken, and even in this instance with 18k on the oil, it remained in grade. Now you could speculate that during this interval it dropped temporarily into the 7cSt range, but even still it's a solid 8.4cSt. Another observation is that SN/SP level additives are clearly sufficient at providing very good wear protection. I have not seen any evidence at all that oils that are highly additized show lower wear. For older engines that's a different story.