I recently purchased a Thule Roof rack to fit the fixpoints on teh roof of the car. However, on taking off the plastic covers, there doesn't seem to be a point for fitting. The rack mounts come with a single bolt but the point that i'd expect to see a nut is covered and painted. Is this just some filler / sealant that's been put in at build to prevent water sitting in the hole? Don't want to break the seal if it starts poring water into the car. Appreciate any advice.