Cake: In large bowl, combine cake mix, eggs, orange juice, cooking oil and pudding mix; blend at low speed for 1 minutes, then beat at high speed 3 more minutes.
Pour two thirds of the batter into a greased and floured 12 inch bundt pan.
Add chocolate syrup to remaining third of the batter and mix at medium speed until well blended; pour over top of batter in pan and marbleize by cutting through batter with knife.
Bake at 350 for 55-60 minutes or until cake tests done.
Cool in pan 10-15 minutes; turn out on wire rack or serving plate to complete cooling.
Top with Chocolate Glaze.
Glaze: In small bowl, combine sugar, cocoa and butter.
Add vanilla then milk gradually to achieve desired consistency and stir until smooth.