I want 37915 to be replaced with "syslog".
You almost certainly don't want to do that, it won't achieve anything meaningful.
The TCPDUMP fragment you show is saying that RCVSPRLN002
is using port 37915
to send a packet to 10.61.0.12
port syslog
which is port 514
. The tcpdump program is using the /etc/services file to translate the 514
into syslog
.
You could edit /etc/services on your monitoring system and add an entry for port 37915 but chances are high that it won't achieve anything meaningful. The rsyslog process on the sending side is just using an ephemeral port. If you restart rsyslog it could easily choose a different one then you'd have to add a new entry to /etc/services and so on.