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I've seen oil analyses that showed a major synthetic was still providing the same amount of protection from the anti-wear additives after 10000 miles. But I change mine at 5000 anyways to be safe. 3000 miles is overkill unless you don't do any highway riding.
Synthetic is better for air-cooled engines. Hotspots can develop that will exceed the average oil temperature which causes dino oil to coke up.
Put a good synthetic in, change at the factory specified intervals, and fugetaboutit.
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