I don't know much about the Castrol Titanium oil you're using. I know that after 10k miles, the oil I use is pretty spent due to detergent depletion and excessive thinning. Why not grab a sample of your used oil at your next oil change and get it analyzed?

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim