fine sand paper works great or you could use An old hobby trick that I do on plastic .... Dot 3 brake fluid. Also lighter fluid supposedly works, never tried that one. I can say the brake fluid one works awesome. Just paint it on or soak it a few minutes, and wipe away or use and old tooth brush too rake across any recessed areas that you can't easily wipe away with. Test first if possible like on the back section of the cover where you don't see, but it works great on model car parts, and they are surely a more delicate plastic.
Thanks all for the tips. I decided to use sand-paper in the areas that were messed up and then blended it all back together. It's hard to see the transition even if you know to look for it. I hope it withstands the test of time so we'll see and I'll post a pic when done. Thanks again.