That kind of small particulate will not be caught by a filter, or two. All IC engines will get dirty oil, there will always be compression gasses forced passed the rings - not a lot, but some. And over time that will change the color of the oil.
A dirty engine, like mine used to be, benefited from synthetic oil and a wash with one quart of ATF for 500 miles (that oil change, it's first one after I bought it, used regular oil). Three years later, a lot of the varnish build up on the cams has gone away. Yes, the oil still gets dirty after 3-4K miles, but that is all right.
You should see the oil in my diesel!!! Black as the inside of a dirty chimney, 10 minutes after changing the oil! And the engine no longer burns oil.
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Keeping it running is better than buying new
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