is it being synced because the contact linked to it is getting synced? Or is it getting synced because it's timestamp is getting updated?
- It is getting added to SFDC because the contact is added to SFDC when you sync the custom object for the first time or when the contact is added to Marketo or when the custom object is created in link with a contact that is already sync"ed
- From this, the custom object will be updated in Marketo only if it's updated into SFDC
So in both your cases the CO will updated in Marketo.
I am a little confused by your answer though.
Just to verify, the custom object has been added to Marketo already.
Both records in salesforce exist already in salesforce, and have been synced to Marketo months previously.
I'm updating something on the custom object in Salesforce, and it should automatically update to Marketo without my having to do a force update on the linked contact.
In other words, Marketo is smart enough to check if the linked objects change, regardless of the contact object it's linked to changes.
Yes, this is it with regards to updates.