The R1 Concepts drilled-and-slotted black brake rotor for 2004 Pontiac GTO is listed as a direct replacement for the rear-left position. The product description lists drilled and slotted braking surfaces with a black finish to match the catalog specification—confirm your GTO's model year and rear-left application to ensure correct fitment prior to ordering.
R1 04-04 Pontiac GTO Rear Left Drilled & Slotted Black Brake Rotor