I have now logged just below 25,000 miles of oil time on this engine. Very happy with Castrol 10W-60 at this time. The most recent results include 4 hours of track time. Copper is down and lead stayed consistent. Good news for my bearings. An interesting thing to note is that all levels are improved from the previous sample, but with 4 hours of track time. The viscosity was almost identical to an oil sample that was taken with almost double the miles. Explanation for this?