You only have to buy clean contacts in spray at any car store or in its supermarket section. You spray with that and then brush. When it is dry, check with magnifying glass that there are no missing tracks or connections between missing faces. If you suspect one, go through a small wire and apply welding on both sides. If you correct everything, you can glaze with a UV paint sold on ebay. If the section is not very large, you can protect with the most economical green nail polish.