Peel grapefruit with sharp paring knife, removing all white. Cut between membranes to remove sections. Arrange grapefruit sections on platter or individual plates. In 4 cup glass measuring cup microwave margarine on high (100%), 1 minute or until melted. Stir in corn syrup, brown sugar and cream. Microwave on high (100%), 4 minutes or until sauce boils for 1 minute, stirring once. Stir in vanilla and pecans. Spoon sauce over grapefruit. If desired, garnish with mint leaves.
Note: Store remaining sauce covered in refrigerator for up to 1 month. To reheat, microwave on high (100%), 1 minute or until pourable.