I am puzzled by your statement that LWP::Debug has a new interface. The version that is bundled with WWW::Mechanize is basically empty.
Well WWW::Mechanize doesn't bundle LWP::Debug, but LWP::Debug isn't exactly empty, the documentation explains the new interface to use, and the old code is still there, unused by LWP itself. Read http://search.cpan.org/perldoc/LWP::UserAgent#Handlers If that works for you, great, otherwise you should use wireshark. There have been many updates and bug fixes to LWP, reverting to a very old version for the sake of old LWP::Debug interface doesn't seem worth it