CREATE TABLE testxml (
  col xmltype
);


INSERT INTO testxml VALUES
 ( XMLType( '<DOCUMENT>
<AUTOSTREAM_DOC_ID>AK_178595</AUTOSTREAM_DOC_ID>
<LEAD_XML>
<SIEBELMESSAGE MESSAGEID="1-1T96JP" INTOBJECTNAME="MM SV CS SERVICE PROVIDER LEAD INBOUND"
 MESSAGETYPE="INTEGRATION OBJECT" INTOBJECTFORMAT="SIEBEL HIERARCHICAL">
<LISTOFMMSV>
<MMSVCSS>
<ID>1-6XI5Z1</ID>
</MMSVCSS>
</LISTOFMMSV>
</SIEBELMESSAGE>
</LEAD_XML>
</DOCUMENT>'));


SELECT t.col.getClobVal() FROM testxml t;


SELECT t.col.extract('//SIEBELMESSAGE').getClobVal() 
  FROM testxml t;