Any persuasive talking points and any other words of wisdom on the subject would be much appreciated.

The sort of questions I would ask would be:

• What happens when we install a new version of Perl?
• What about code that relies on the existing behaviour - you did check that didn't you?
• How do we track that change when we install our software on another machine - you did check it into source control didn't you?
• Can you show me the automated test that highlights the bug in the module (fails with the system module, passes with your fix)?