How common is it for coyote motors to get bad valve seals? My cyl 8 keeps misfiring and fouling the plug. I changed the coil and nothing. At first i was scared it was my piston ring but the symptoms are pointing towards valve seals. The only time i see any smoke from my exhaust is a quick puff when i turn it on in the morning. Its also intermittent so it will be misfiring pretty bad and if i turn it off for a minute or two and turn it back on, it runs fine again. I think im burning a bit of oil too. So what do you guys think? Car has 92k miles