pg_dumpall failure - could not access status of transaction

I am attempting to get a handle on the corruption that caused
the following error:

pg_dump: SQL command failed
pg_dump: Error message from server: ERROR: could not access status of
transaction 3183024
DETAIL: could not open file "pg_clog/0003": No such file or directory
pg_dump: The command was: SELECT description, classoid, objoid, objsubid
FROM pg_catalog.pg_description ORDER BY classoid, objoid, objsubid

I've run pg_filedump on all the files with the name = oid from:

select oid,relname from pg_class where relname='pg_description';
oid | relname
------+----------------------------
2609 | pg_description

but there are no errors reported.

I'm (obviously) lost here - what is the correct way to track down the
appropriate file and record to point pg_filedump at to view any
corruption?

Robert