Hi: I would sand the finish down with 220 grit sandpaper, very lightly to take off the rough spots. Clean it with a shop vac. and then use rags dampened with water to remove any dust. Then apply a clear high gloss polyurethane. If the original finish is completely dry you could use either water base poly or regular. I use foam throw away brushes, they don't leave marks. A couple of coats should do it. Woodnut65