feeling dumb. Can't map 2 fields...

Yes, you can do this.

See: https://community.marketo.com/MarketoArticle?id=kA050000000KypG
AND

https://community.marketo.com/marketodiscussiondetail?id=90650000000PTSEAA4

You may want to confirm your Marketo User can see the original SFDC fields. If NOT, then change the security/profile for that user. Marketo will see the fields and sync them in a few minutes or a few hours.

I might not have been clear, the fields both were created in SF and sync'd to seperate Marketo field names. I had to open a support ticket with Marketo since they have to create the merge on thier end.

They were able to take this:

and remap it to:

We've had to do that on occasion as well.  I'm not sure if there is a time limit that you have to create both fields with the same name before Marketo assumes they are different and synchs them with different field names or what.  It would be great if someone from Marekto could respond about this.

are they mapped in SFDC?  in lead app set-up there is funtion to map lead fields to contact fields.  If this is not done it's a good idea to map otherwise marketo will see them as 2 fields and you may loose information in SFDC when the lead is converted.

Sorry for the delayed response on this issue but hopefully I can clear things up. At present the only time an end user/admin will have the ability to edit Marketo SFDC field mapping is during initial setup, after you sync over all your sfdc fields but before you sync over all your SFDC data you will be able to drag and drop some fields in the filed mapping section to create a 2:1 mapping. After your sync is up and running new fields that you create in SFDC and expose to the marketo sync user's profile will be automatically create in Marketo. If you create a lead field and a contact field with the exact same label then a 2:1 mapping should be auto created, 1 Marketo field will map to the SFDC lead and to the SFDC contact field. You will need Marketo support's assistance to merge/remap fields if the spelling is different or if one fields is on the lead object and the other on the account object.

I have a feeling that Joe's fields didn't auto 2:1 map because even thought the api name are identical it looks like the field label for the lead object was "Message" whereas the field label for the contact object was "Lead Message".

Thanks for the clarification about Lead and Account fields with the same label won't auto 2:1 map.  This explains why our new SFDC Lead fields with a corresponding new Contact/Account field don't always auto 2:1 map.  Mystery solved!