I think this will do the same thing a bit cleaner:
@nodeselect
@if:Set UTILITY=Sync
Set UTILITY=Off
@if:else
Set SOURCE=Left
Find SYNC NOAUTORUN FROM {filepath$} TO {filepathdest$}
That will open the Sync panel for the selected folder on each side, with the left always being the sync source. Other sync settings will be as they were last time it was used (but you can add arguments to specify them, or a saved preset, if needed).
When clicked again, it'll hide the sync panel.