Any entered or unentered merchandise (except merchandise under section 557, Tariff Act of 1930, as amended (19 U.S.C. 1557), but including merchandise entered for transportation in bond or for exportation) which remains in Customs custody for 6 months from the date of importation or a lesser period for special merchandise as provided by § 127.28 (c), (d), and (h), and without all estimated duties and storage or other charges having been paid, shall be considered unclaimed and abandoned.