I have a couple of Nikon F bodies. My mentor suggested always using a couple of pieces of black tape over the sides where the back joins the body. On mine, the commonplace modification was made for accommodating the MD5 motor drive. That resulted in the corners of the back being broken off. This made the light leaks worse.

If you can't install a good light seal kit immediately, do know that black tape will keep your camera functional for a while. Tape is not convenient, but is better than light leaks on your film.