Combine all the ingredients, except sesame/vegetable oil, for the marinade in a bath solution and place cleaned duck in it overnight.
Hang dry and rest for at least 2 hours. Hang duck in smoking oven with hook on the upper neck.
Place the camphor wood, brown sugar, tea twigs, if available, on a pan at the base of the oven and heat oven to 350 degrees F. Some recipes call for tea leaves but tea leaves in the sugar/camphor mixture does not add that much tea flavor to the ducks. Roast the duck for approximately 40 minutes, but depends on size of duck, type of oven, etc. For best results for a crispy skin, the last 5 to 10 minutes should be at 400 degrees F, with a final basting of sesame/vegetable oil on the skin of the duck. Duck can be flashed in hot oil to finish, if timing for service is critical.
Cut and serve hot, with buns and sauce, optional.