Best you van do is a damp magic eraser(any store brand or Mr.Clean) and a little APC like LATA or whatever you use to clean you tires will clean And smooth the plastic. Then use a coating like a GTechiq C4, or a trim protectant like Ultimate/WG Trim sealant. Using quality tire gel can help as well but may only last a week or two; or until it's rubbed off by whatever's doing the damage in the first place. I'll tell you, a client/friend of mine used mix of Mother's Back-to-black and black shoe polish on his newly purchased pre-owned tundra and it looked pretty good but will stay a little greasy to the touch and maybe glossier than you'd like. To cure the issue thouogh, so t doesn't keep occurring, you can apply mole skin or some stick-on Velcro pile to whatever's contacting the plactic.
