My brother took his in for service and the mechanic told him that the plugs work loose because the head design increased the difference in expansion rate between the aluminum head and the steel spark plug He told him to just check the torque on his plugs every 3K or 4K and he'd be fine. He's been doing that for 10 years and not a single problem, so I'm doing the same on my 2018 just to be sure.
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