A damaged outer tube may be repaired by any Federal firearms licensee qualified to perform gunsmithing or by the registered owner. The repair may not alter the dimensions or caliber of the silencer, except that the length of the outer tube may be reduced, as set forth above. The repair may not be performed if it results in the removal, obliteration, or alteration of the serial number, as this would violate 18 U.S.C. § 922(k). In that case, the silencer may be returned to the registered owner in its original, damaged condition or destroyed. A replacement silencer must be registered and transferred to the registrant of the damaged silencer in the same manner as a new silencer, subject to the registration and transfer procedures of the NFA and GCA.