Somewhat related for those with exposed metal.
I recently dropped my lid on concrete (whoops...). The lip had some exposed metal. What I did was take some crisco shortening and apply generously to the exposed part. The next time I grilled I left the exposed part with crisco on it over the coals for a while after I was done (not sure if this part is necessary).
When it was all said and done the exposed part was now black and "seasoned" if you will. Not sure how long it will last, but I'll keep an eye on it.