Hello, rbatte1.

Without having an actual input or output representative example from you, I do think RudiC has shown you a valid indication of what it is possible. Definitively, you do not have the need to grep for it.
If is of any help to decipher what it has been shown, allow me to break it in pieces.
Essentially, there are two pieces to process each line, based on the format structure of /var/log/syslog

Code:

split ($5, U, /[[]/); # it divides field 5 into smaller parts ([ is the separator) and creates an array to capture the pieces using a variable named U.
T[U[1]] = $1 " " $2 " " $3 # builds an index using the variable T where the index is the first element of U, the split done before.

Once all lines has been processed, display the result:

Code:

END {for (t in T) print t, T[t]} # iterate over the index and display what's recorded.

Since, this is done for each line, you'll get multiple hits.
If you want to narrow it down to a particular criteria, let's say: "Active transaction started"

Code:

awk '/Active transaction started/ {split ($5, U, /[[]/); T[U[1]] = $1 " " $2 " " $3} END {for (t in T) print t, T[t]}' /var/log/syslog

Limiting the index to only those lines that contain the match.

If you were to post a representative example, I am quite sure we could provide other alternatives, as well.
Also, you might be interested in knowing about an open source project named: ELK
Which it does an amazing job at dealing with all sort of information on logs.