One quart of vinegar -- with 20 percent acetic acid -- mixed with 4 ounces of lemon juice will kill the above-ground portions of the weeds and grass. The foliage, flowers, buds and stems will wither, dry and die, but the weed's roots are left intact. For a tougher weed and grass kills, combine 1 tablespoon of 20 percent vinegar, 1 tablespoon of gin, 1 quart of water and 1 teaspoon of dish soap. This mixture kills the above-ground and below-ground portions -- including roots -- of the weeds.
From experience, I usually boil a pot of water (6 to 8 cups ) and let it cool down a little bit. Then I get white vinegar(avoid the fruit vinegars) and add about 5 cups of it into the water. Then I would let the shirt soak in the white vinegar and water for about an hour. Vinegar is a mild acid so it acts as a loosening agent for the stain. After your remove the shirt from the pot in the hour, wash as usual. (preferably with a stain removing detergent like tide) The link below provides other methods of removing moss and grass stains. I hope I helped! Going Green Grass and Moss Stains
It can be repainted, using spray on, High Heat Grill Paint. Which, you can find at any home center or hardware store, in the paint department. Krylon makes one, as does Duron. I personally like Krylon, as it seems to cover better.
You will need to thoroughly clean the surface of any grease, rust, loose paint, etc. Then wipe the the area to be painted with denatured alcohol and then wipe off any remaining residue before spray painting it. Several light coats is much. much better than two heavy coats. Allow each coat to thoroughly dry, before applying the next coat.
Do not use the grill for 48 hours, after the final coat of paint has been applied.