They do make clear coat in spray cans but I would suggest that you take it to a body shop. Since the clear coat could be enamel, lacquer, or polyurethane, it is best to know what your original paint is. A body shop can make that determination and then mask off the area, prepare it properly, and apply a new coat of clear. Chance are, if the base coat has deteriorated, and has noticeably changed colors, that the new clear coat will protect it but it still will not match the other areas of the coach that are the same color.