What makes you think it is teak , unless it is Japanese, Chinese. Teak
boat decks are cleaned with a mild acid and oiled, teak trim is sanded
and varnished. I would degrease it with alcohol and thinner then sand
and oil or varnish. If it is an antique leave it alone till a pro looks
at it. Walnut or Birch are common US gunstocks, never Teak.