I had the same issue... A slave server had missing wal_files... and it wasn't synced.
I had to re-sync all the DB, by running the pg_basebackup command....
So.. basically, what I did is:
1 - Ensure that the wal_files are being inserted into the slave
2 - Backup the recovery.conf, postgresql.conf and pg_hba.conf
3 - Delete all the current data folder, by doing: rm -rf /var/lib/pgsql/9.2/data/*
4 - Running the pg_basebackup command to re-sync the DB from another slave to the slave that I wanna fix
5 - Replace the .conf backup files into the new data folder
6 - Start postgres
And it worked nice....
Patrick
