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- Plano, Texas, USA
Replacing spark plugs at the recommend 75,000 miles is for preventive maintenance. You can also not to change the factory engine coolant at recommended 120,000 miles or 10 years without immediate issues, but eventually it would cause problems. Another example is the ATF change. Although you believe its not necessary, but those used ATF analysis reports from BlackStone show the ATF does wear out over time.Fair enough, I'll say that if you don't have a problem, don't change them.