I suggest that you increase the number of holding screws. Take the screws out and source some that are same length but perhaps slightly bigger width, if possible. Re-fit the rail and mark some extra screw points. Remove rail and drill new holes. Re-fit rail and screw new screws in to drilled holes. This will make new holes...Remove whole thing and put some silicone adhesive in all holes and then refit rail. Leave for the stated time and try it..I had a similar problem in my previous van and this remedy worked.....Hope it helps you.......