how then is it possible for CPAN to be installing stuff where perl cannot find it?
Is the "perl" that runs the Makefile.PL the same "perl" that is run when you try to use the module that CPAN has just installed ? If, for example, /usr/lib/perl runs the Makefile.PL, then the module being installed will be located in a place where /usr/lib/perl can find it, but /usr/local/lib/perl won't be able to find it.
If it is the same "perl" in both instances, and the modules are being placed where they cannot be found, then something is seriously amiss with Config.pm's %Config.
that was the problem! of course. the script points to /usr/bin/perl which is the old custom built perl. I removed that and symlinked it to the system perl, now it all flies.