Hi,
You should be able to find IPSEC / L2TP log messages by typing a logread command. Make sure you didn't restart your router as the log is cleaned after every restart.
Also, if you want a more readable format, you can just download a troubleshoot file in which you will find the same log. To do that go to System > Administration > Troubleshoot and download Troubleshoot file there.
EB.
