De Duplication based on Custom Field?

Hi there,

We have had our instance for ~1 year and we've got some data hygiene issues. Since the majority of the data in our instance is from legacy data through list uploads I've noticed that we have a lot of duplicates stemming from syntax errors and incorrect email addresses that have led to contacts being duplicated upon re-load of the corrected email address. I was hoping to use our CRM's customer ID as a way to de-dupe these contacts in Marketo but from the information I could find here (from 2014) that doesn't appear to be possible. Is there a way to find possible duplicates based on custom fields? Has anyone found a way around this?

Thanks,

Jenn