If it's squishy like a rubber sponge, then it's OEM. If it's hard like fiberglass, then it's aftermarket. Yes, there will be an ugly spot that you would need to get an NA third brake light panel for if you are going for the spoiler-less look.
"Stance: cuz goin fast cost money yo (n/m) - ZiNnYc 08/09/12 18:23:42"