I think TCP version of syslog is not supported by JunOS on HE devices. I have used tcp syslog feature supported Cisco ISO using catalyst switches and also used it on ScreenOS.
syslog config "10.10.10.10" transport
However, a workaround can be a syslong-ng machine (which support tcp syslogging) working as Syslog gateway, transforming UDP Syslog to TCP Syslog; i.e.
SRX -----<trust>--------- Syslog-ng ------<untrust>------ NMS
kind regards