Have you tried to use DBMS_LOB.CONVERTTOBLOB@remote(....)
But you probably want to get some sort of checksum of the remote CLOB to see whether they are getting a characterset conversion when they are inserted/updated from whatever original external source. That is, if the client characterset, when the insert is done, is different from the database characterset, the problem may have already occurred before you do your select.
Edited to add.
The closest I can come up with requires some objects on the other end of the link.
Firstly a function that does the conversion at the remote end.
Secondly a view that presents a 'BLOB' view of the data.
This uses a dummy table (based of v$sql as it was the first CLOB I could find). No reason I can see that you can't simply pass the CLOB as a parameter to the function.
create or replace function ret_blob return blob is
cursor c_1 is
select sql_fulltext, sql_id, length(sql_fulltext)
from v_sql
where sql_id = 'bzmb01whp36wt';
rec_c1 c_1%rowtype;
--
v_blob blob;
v_dest number := 1;
v_src number := 1;
v_lang number := 0;
v_warn number;
--
begin
open c_1;
fetch c_1 into rec_c1;
close c_1;
dbms_lob.createtemporary(v_blob, TRUE);
--
dbms_lob.CONVERTTOBLOB (v_blob, rec_c1.sql_fulltext, DBMS_LOB.LOBMAXSIZE,
v_dest, v_src, DBMS_LOB.DEFAULT_CSID, v_lang, v_warn);
--
dbms_output.put_line(':'||v_warn||'>'||length(v_blob));
--
return v_blob;
end;
/
create view rblob as select ret_blob from dual;
Then, from the local database, do a
create table t as select ret_blob from rblob@remote