I've seen people say that if you use SXTH's spare ECU that should you need dealer work you swap back to stock ECU/parts and they'll never know you were tuned. How true is this? I was always under the impression that mileage stays with an ECU. So if I were to put a SXTH ECU on at 5k then need warranty work at 40k my stock ECU would only show 5k miles. Is that how Hyundai works, or can you genuinely run aftermarket mods without having to worry?