I got this one-liner from here

 perl MFile::Find=find -MFile::Spec::Functions -e 'find {wanted=>sub{p
+rint canonpath $_ if /\.pm\z/}, no_chdir =>1}, @INC;'
[download]

And one way to do this is to run this on your target, vanilla installed instance and compare the output of your existing, modified system for differences.