There is no uninstall log (to my knowledge). There are a host of install/uninstall apps, Revo Uninstaller
is 1 of them. I would try installing Revo then re-installing Opera, uninstalling Opera using Revo, then clean installing Opera.
Doing the install/uninstall/clean install will give Revo a basis to work on and hopefully it'll produce an install/uninstall log for you