Modification and Exchange All or a portion of the Classes of REMIC Securities specified on the inside cover page may be  exchanged  for  a  proportionate  interest  in  the  related  MX  Class  or  Classes  shown  on Schedule I to this Supplement. Similarly, all or a portion of the related MX Class or Classes may be exchanged for proportionate interests in the related Class or Classes of REMIC Securities and, in the case of Combinations 7, 8, 9, 10, 14, 15 and 16, other related MX Classes. This process may occur repeatedly. Each exchange may be effected only in proportions that result in the principal and interest entitlements  of  the  Securities  received  being  equal  to  the  entitlements  of  the  Securities surrendered. In  the  case  of  Combinations  7,  8,  9,  10,  14,  15  and  16,  the  related  classes  of  REMIC Securities may be exchanged for proportionate interests in various subcombinations of MX Classes. Similarly, all or a portion of these MX Classes may be exchanged for proportionate interests in the related REMIC Securities or in other subcombinations of the MX Classes. Each subcombination may be effected only in proportions that result in the principal and interest entitlements  of  the  Securities  received  being  equal  to  the  entitlements  of  the  Securities surrendered. See the example under "Description of the Securities – Modification and Ex- change" in the Base Offering Circular. A Beneficial Owner proposing to effect an exchange must notify the Trustee through the Beneficial Owner's Book-Entry Depository participant. This notice must be received by the Trustee not later than two Business Days before the proposed exchange date. The exchange date can be any Business Day other than the last Business Day of the month. The notice must contain the outstanding principal balance of the Securities to be included in the exchange and the proposed exchange date. The notice is required to be delivered to the Trustee in writing at its Corporate Trust Office at Wells Fargo Bank, N.A., 45 Broadway, 12th Floor, New York, New York  10006,  Attention:  Trust  Administrator  2004-039.  The  Trustee  may  be  contacted  by telephone at (212) 515-5262 and by fax at (212) 509-1042. A fee will be payable to the Trustee in connection with each exchange equal to 1/32 of 1% of the outstanding principal balance (or notional balance) of the Securities surrendered for exchange (but not less than $2,000 or more than $25,000); provided, however that no fee will be payable in respect of an interest only security, unless all securities involved in the exchange are interest only securities. If the notional balance of the interest only securities surrendered exceeds that of the interest only securities received, the fee will be based on the latter. The fee must be paid concurrently with the exchange. The first distribution on a REMIC Security or an MX Security received in an exchange will be made on the Distribution Date in the month following the month of the exchange. The distribution  will  be  made  to  the  Holder  of  record  as  of  the  Record  Date  in  the  month  of exchange. See "Description of the Securities – Modification and Exchange" in the Base Offering Circular. S-19