Lead Source workaround in SFDC

You can't edit the Lead Source on a Contact?

you can't edit any fields on a lead once it's been converted. the lead object becomes locked for that record. so, if say you have a lead source that's wrong, and then the lead gets converted before you fix it, your lead reports in SFDC will be wrong, because you can never go back and fix the lead data. it's a 7-year old issue in SFDC. There are a number of workarounds as described by commenters on the thread https://success.salesforce.com/ideaview?id=08730000000BprXAAS . some people stop using the lead object altogether, and others create a custom lead object. That doesn't work though when you're integrating with SFDC. I'm hoping there's a way to track the lead source in Marketo independently from the SFDC fields, so that the lead source can stay consistent and editable as the lead becomes a contact, and also so that I can run a single report that includes both leads and contacts at various stages.