Alison,
I wasn't able to export the SFDC ID directly and it's my understanding that this is a restricted field (I'm surprised that your colleague is able to export).
Following Jason Long's advice, we have a custom field set up to duplicate the SFDC ID field, which IS exportable. We call it "CRM Key" and the rule is:
Value: is ‘{{lead.SFDC Id}}’
Seems redundant, but it's the workaround we've been able to successfully use.
I hope this helps.
Dane