Greying black plastic trim

If you have painted areas next to the plastic, apply a masking or painters tape over the paint, to stop the chance of it being marred. Apply water to the bar and gently rub over the plastic surface till the greying is gone, turn the bar to a new portion reasonably often, dry off and inspect to see wether it needs further applications. Once dry, you can finish it off with an application of Vinyl Revival.