Those are usually held together with a plastic rivet that is melted to fuse the two parts together. Since they are already NG, then give it a try to see if you can get the two halves apart. I suggest a Dremmel tool, and a lot of patience. I have successfully taken apart plastic parts, cleaned them, and then put them back together with silicone. The good part, is that the next time you want to clean them, they come apart easily. Just don't use anything that will melt the plastic trying to remove the paint.