The fact that your log doesn't contain anything simply means that it didn't find in the TCP payload some data starting with /siebel. look at the findstr command definition
Click here
if you want IP data to your log you may use [IP::client_addr], [IP::server_addr]:
Click here
You should have a look at the iRules wiki to find other data you may wish to troubleshoot:
Click here
A monitor with only GET will at least ensure the service is open and available. If you want to ensure for example that the request is fine then you may add 200 for example to the response analysis. I'm not a siebel person either so can't say what may be the best to monitor such a service!
HTH
Nimbostratus
