Just my two cents worth, I make sure first I have a really good cemented seam, preferably with a little bead of plastic coming out. Let it dry, then sand it. Any areas can be checked with just about any color, green or brown even, some people exclusively use silver or aluminum though, it's up to you. I find that drawing a line of super glue over the area is a great way of filling seams. You can accelerate it drying by dribbling some water over the area where the super glue is, sand almost immediately afterward. Let the seam take what it wants and remove the excess. Hope this helps some. Russell