|Do you know where your variables are?|
I had a similar problem and followed a different path: in my virtual Mint 15 I installed a new perl (5.14.4) over the native perl 5.14.2 and apt-get started throwing errors, mainly...
...dont't find ... Debconf/Db.pm in @INC ...
So @INC has lost the directory which holds that pm, but it (and other pms) were still in the system.
Solution: find Db.pm
find . -name Db.pm -print
Then I go to one of the dirs in current @INC and create a symlink
ln -s /usr/share/perl5/Debconf Debconf
'et voila', I managed to upgrade flawlessly, apt-get is working
Don't know if it would work if both perl major versions were different (here is 5.14 for both).