Funny this should come up. I got gum on the lower black/grey part of the bumper under the painted section and asked the car wash to remove it for me. Well they did with acetone an it turned to plastic a light grey to white color. I tried everything short of replacing it because it bothered me so much, the last this I tried before buying a new piece was the informercial stuff 'wipe new' and after the second coat it is perfect and had been for about a year with no fading. For $20 it was worth it and does not look bad, if you look really close you can see were the gum was, but i would have to show you.
Hey guys all good ideas for sure! My garage door actually took a chunk of the rubberized black coating out so I'm looking for some type of paint material to touch up with.
The wipe new idea may help though so it's worth a shot! I had no clue a heat gun could do that to black trim....
Might not help with filling in a chunk missing from the plastic, but this stuff is one step above, in severity, a product like Back-to-Black, Ultimate Black, or VHT: https://www.amazon.com (commissions earned)
Never used it before, but the reviews seem pretty positive for you to decide if it will work for you. More of a dye based approach than a restorative/cleaner. Lots of before and after pictures from users too.
I know it won't help in this situation but a tip I found out by accident If your trim on the bottom of the bumpers and around the wheel wells starting to look faded to a white or a gray color use a magic eraser and you will see all the embedded dirt come out and your trim will like new again then you can use a dressing to seal it.