Information
Using a syslog server provides a means to collect, analyze, and store device logs off-box in the event the source device fails or the original logs are compromised in some fashion, whether intentionally or via error. Most syslog servers also provide a means of searching, reporting, and alerting which greatly assists in the administration of the firewall.
This should ideally be the interface closest to your syslog server.
NOTE: You will need to change 'Syslog_Source_Int' to the appropriate interface from which you need to source your syslog traffic.
Solution
You may navigate to the following ScreenOS menu location: Configuration > Report Settings > Syslog