If you are emmigrating back to SA as a returning citizen and have lived out of the country for more than a year and owned the vehicle for more than six months then you don't need to pay any import duty, you do however have to pay an ad valorem tax of 15%. You can take back up to three vehicles in your life but only the first one is exempt from Import Duty. The other two you have to pay 40% import duty on top of the ad valorem tax. The values are based on the value of the vehicle from the country which you are bringing it in from, not the value in South Africa.