I have a 912uls with 580 hours. I run ethanol-free auto gas 90% of the time. When i use avgas i add Decalin. For the last two annuals i have seen scaly white material covering most of the piston heads when looking through the spark plug holes. The engine runs fine and the plugs look good after 100 hours (though i replace them at every annual). What is going on? Is it a problem?


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