You didn't list your XS modules. But if I were hunting for the memory leak and Devel::Leak wasn't helpful, I might start looking at bug reports for those XS modules (both current, and resolved if I'm using an older version of a module). Additionally if I'm looking at an older module I would also check the Changes file for that module to see if there was something fixed in a more recent version. ...of course if possible it would be a good idea to make sure all the modules are updated to their most current versions, especially with XS, though with such an old Perl you would want to test interoperability before upgrading in production.