It's not the valves that are the problem, it's the factory tune. It is well known that the OEM map has a flaw and can cause burnt valves.
That's from my Tuner, he found the flaw a few years back.
178,000+ miles, 5/20/12 new ej257 short block, 8/20/11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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