Hi! A bit correction: SL and SLC category never was S- class. SL mark mean SuperLeicht ( Superlight ) for 'sport' Benz. S-class coupes only the SC and SEC models. Letter 'S' mean Sonderklasse or Special class Letter 'E' mean Einspritzung or Injection letter 'C' mean coupe. In the 70's had got the C116 SC/SEC S-class coupe ( made from the legendary W116) after in the 80's the C126 SEC (made from the W126) later the C140 (made from the "Whale" W140)