View details of SalesForce Sync failure?

You can view the sync failure from Marketo to SFDC when you click on a lead's Activity log.  For instance one of the big sync problems we had was a phone, mobile and fax formatting restriction on SFDC, which prevented leads from syncing from Marketo to SFDC because the formatting has to have a +1. Saw that on the activity log and that's how I found out that we had a problem.  It was since removed from the user and all is working fine now. 

Is there a way to locate all the records that are are having "sync" failures? 

There isn't a specific criteria to locate SFDC sync failures that I can find, but here are two approaches to get close to the right number:

 

1. If you by default sync all leads to SFDC, you can create a smart list based on the criteria "SFDC Created Date is empty".  
2. If you have a specific campaign that syncs all leads, you can check the results of that campaign; you should find there the failure notifications.

 

A third approach is to compare the number of people you have in a program/campaign with a success. Compare that to the number of members you have to the synced SFDC campaign.  If there's a difference, then there's a sync failure. Sort the members in a way that's easy for you to cross check who is missing.  Check one of the lead's record that failed to sync and look at the activity record and you might be able to find the cause of the failure.  

It's really not that painful, but that's the other way I detected that there was a sync problem.