I've been following this thread closely because it reads like a good mystery novel. And the questions and suggestions have all been intriguing. I'm 70 years old and have hands on experience with internal combustion engines since I was about 10. My first bike(?) was a 1964 Honda supercub C90. I have to say that in all the years of observing used oil I have never seen that grey color you photographed. For sake of simplicity I burn the Honda GN4 10/40w. And I only burn non ethanol gasoline. My '86 250 has a little over 12,000 miles and I change the oil every 1,000 miles. The oil is dark at that point but not, say, coal black. Others on this forum have their own preferences for oil which I would not dispute. However, I'm very curious about the effect (of whatever is contaminating the oil) on the oil's viscosity since that will severely impact the life of the engine, transmission, and clutch. From what I've read so far, I would agree with Guba's point about the grey color resembling aluminum. But in the second and third pics there appears to be a mixture of what I consider to be the normal dark color of used oil, and the grey-ish color. As others have mentioned, it doesn't resemble typical moisture contamination. It will be interesting to see what your son says about clutch performance. Good luck Sherlock!