Good advice above. I would clean it lightly with Murphy's and maybe steel wool and mineral spirits if necessary. Then apply Bullseye Amber with a rag ball with a few drops of linseed on it. Dip the ball into the shellac and rub it on in small circles. This is essentially French polishing except you are rubbing out the worn old finish. The alcohol in the new shellac will dissolve the surface of the old. After the final pass rub it out with rottenstone mixed with linseed to get rid of swirls and imperfections. It will look good and still be original underneath.
As to the original finish, I don't think they could have dipped it in shellac because it would dry fast, run and make a mess. They may have dipped in linseed then brushed or sprayed the shellac.
