I filled the gap between the spar and the leading edge with Superfil. My kit did not come with Superfil so I tried the Hysol provided first. This was not as easy as the Superfil since it is harder to spread consistently and it is way harder to sand which is not good considering that you do not want to scratch the aluminum spars in any way. I also used a scrap piece of plywood to form a scraper that matched the contour of the edge.
