In a large bowl, combine first seven ingredients. Add oil, buttermilk and eggs; mix well. Fold in plums and nuts. Pour into a greased 13-in. x 9-in. baking pan. Bake at 325° for 40-45 minutes or until cake tests done. Remove from oven and punch holes in top of cake with a wooden skewer or pick. Immediately combine glaze ingredients in a saucepan. Bring to a boil and boil for 2 minutes, stirring constantly; pour hot glaze over warm cake. Cool in pan. Yield: 12-16 servings.