I believe you can do that with Streaming Viewer if you don't want to do a tcpdump in a terminal window.
Streaming Viewer lets you add filters and columns, and view the packet data.
The streaming events are real time for syslog I believe. If you scroll to the right in the display you will see the raw packet data. This is not obvious but the display expands as you scroll.
The fully parsed message is not displayed but if it is parsed then the rule it matches will be shown. Source and destination also look correct.