The old varnish is nothing to worry about,, its the patina of the wood itself that needs to remain !! Many times the old varnish will crystalize and darken and that does not help its appeal or value !! Just get someone that knows what they are doing to repair it !! And don`t let them sand it at all !! There are ways to clean & restore it that will not damage it !! Its no huge value but still an interesting chair !!