This list is not official support for Balabit's products and I am not really an rsyslog expert, but let me try to help.
I think the issue might be related to "framing", e.g. syslog-ng configured to expect framing whereas rsyslog not doing it. This page:
contains a parameter which is TCP_framing that defaults to "no".
Thanks Bazsi, appreciate the hint, you put me on the right track.
For those that come behind me, the major issue I found was the allowed data in the conf file - there didn't seem to be any documentation at all about what values TCP_Framing could take. Case insensitively the following didn't work: yes, true, on
Trial and error/guess work discovered that the correct syntax to get this working is "octet-counted"
[root@host02 /etc/rsyslog.d]# cat tcp601.conf
*.* action(type="omfwd"
queue.type="LinkedList"
queue.filename="example_fwd_tcp_601"
action.resumeRetryCount="-1"
queue.saveonshutdown="on"
template="RSYSLOG_SyslogProtocol23Format"
target="10.126.19.45" Port="601" Protocol="tcp"
TCP_Framing="octet-counted")
Cheers
L.