When rewiring my various electrical additions, I also took the time to remove and clean the OEM air filter. These photos were taken with about 16,000 miles on the odometer. The filter had already been replaced during the 12,000 mile service so wasn't very dirty. I used compressed air from far enough away to prevent collapsing the paper element to "clean" the filter. Pretty standard stuff.
More interesting was the air box.
The pattern is a collection of very fine dust which has not made its way past the filter. It's probably not enough to worry about, but is enough to make me wonder if one of the various after market filters would do a better job. I assume that the pattern is a result of moisture getting to the inside of the air box and forming the dust patterns like ice crystals on a window pane in the winter.
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