A member requested explicit allowance for rear deck spoiler a couple years ago. Response in March 2012 Fastrack:

"NR: Thank you for your letter. Rear deck spoilers are not compliant in Super Touring per GCR 9.1.4.D.2"

GCR Technical Glossary:

Wing – An aerodynamic attachment to the structure of a car specifically intended to generate downforce from the action of air flowing over the upper and lower surfaces, creating a pressure differential.