(a)New bonds shall be required under sections 5173 and 5175 in case of insolvency or removal of any surety, and may, at the discretion of the Secretary, be required in any other contingency affecting the validity or impairing the efficiency of such bond.
(4)without payment of tax for exportation, after making such application and entries, filing such bonds as are required by section 5175, and complying with such other requirements as may by regulations be prescribed; or