I worked for a Specialist Antique Clock restorer back in the 70s he only used an authentic fish glue which was constantly being 'cooked' in a heated tub.........it stunk the house out. He bought cheap period pieces of antique furniture from Auction houses to piece in pieces of period wood. When he had finished you could not see any of the work that he had done it all looked 17th and 18th Century patina. He said that he had numerous long case clocks in Museums that he had restored .
Don't sand it down for heavens sake you'll make it completely worthless. Nobody would want to buy a antique long case clock that looked like new . Conservation rather than renovation is the way to go.