Im in the same boat. I have a nick in the plastic front bumper. I tried the Langka sysyem and it didnt work as the scratch in the plastic is to deep and because it is plastic, it is burred up around the edges of the nick. It looks terrible and although it isnt big it is in a place on the edge of the bumper that really shows it.
Other than having it filled and sanded and painting the entire bumper , I see no way of fixing this. So i have touch up paint on it to hide the black plastic colour ( my car is grabber blue) But I am leaving it alone although it drives me nuts.
2011 GT. Grabber Blue. Procharged. 3:73 manual.Billit LCA's. Corsa Extremes. GT 500 wheels. Racemaster DR's. T-56 Tremec. Dynotech DS . Centerforce DF. American Racing headers/high flow cats 560 rwhp.Donny Walsh tuned
2012 Pony Package. Race Red.3:31 automatic.BBK longtubes and catted X.FRPP Sport axlebacks. BBK throttle body. Dynotech DS. Brembo wheels and tires. Strut tower brace. Airraid CAI. Bama tuned.