Oh Ok where the vertical stab (v stab) is attached to the fueslage (fuse)?? Use a flux brush (small metal brush with bristles available at the local Hardware store) and apply some 30 minute epoxy around the edges on both sides. Any other way would require carefully cutting the Vertical Stab off and re-applying the epoxy. Other's might suggest removing it but I have had good look by using the 30 minute epoxy without having to cut it off. 30 minute epoxy is strong stuff. Try and force as much as you can in between the fuse and the v Stab. Be sure to check your 90 degree aligement. You want to check it every few minutes while the epoxy cures. After 30 minutes it will be set and no adjustments will be able to be made. Any excess epoxy can be removed with rubbing alcohol prior to it setting up. From what you have described this method should work for you.