YOUR OIL IS TOO THIN. The oil control ring package on these cars is terrible & they were typically set up loose from the factory. Change it to mobil 10w40 synthetic or equivalent. I did & my car quit smoking. Plus, you don't have cats to help burn off excess exhaust emissions. If the thicker oil doesn't help, get a catch can to help filter the excess oil from the intake charge. The pcv systems on these cars sucks *****! A lot of oil always gets pulled through the system, into the intake, & down to the combustion chambers where it then burns off & smokes out the exhaust. My Z06 was a terrible oil burner until I took these steps. It only had 31,000 miles on it at the time. After all this, definitely sea foam it to clean up your combustion chambers. The one cylinder that is worse than the others probably has excess carbon build up on the rings. The sea foam will help it. Good luck!