You can contact a Service master type company or one the re-mediates fire damaged homes as they have a spray that they apply over charred wood to seal and eliminate the smell form the charred wood. I am not 100% certain but do not see why something like this will not work.

Clear shellac may do the trick. Shellac is often used to seal in smoke odors and pet urine stink. (Is it possible that what you're smelling is cigarette or cigar smoke? The age of the house may make it likely and that really reeks!)

As always, test first in an inconspicuous spot as the finish on the paneling may be shellac and a new coat could disturb the color by re-liquifying the shellac, which is often tinted. (You could tint new shellac, too, but it sounds as if you like it the way it is now? It does darken with age.)

You can test to see if it is shellac by using water which will mark shellac. Denatured alcohol will dissolve shellac. Mineral spirits would dissolve varnish - but not shellac - and wax - so you might test with that as well.

But if you decide to go ahead, you might try buying shellac flakes and mixing it up for the job. There are varying levels of sheen in shellac as well. Old shellac sitting pre-mixed with alcohol (its solvent and carrier) in a can can go bad so fresh is always better and stuff in hardware stores and big box stores may have been sitting around as it is not a really popular finish in these days of poly-everything.

Be sure to ventilate the room while applying as it will give you a cracking headache (and probably kill off some brain cells) to be closed up while working on it. Once its dry it doesn't give off odors as the alcohol evaporates completely. Shellac is a bear to apply during periods of high humidity, so wait for late fall, when it's dryer and you can still open windows (leave screens in to inhibt bugs getting caught in the still-drying shellac.)

HTH,

L.