Those instructions should work, so my best guess is that you may not have hidden the correct field. I would double check the API name of each field in SFDC and Marketo to make sure you have hidden the correct field.
Hi Devraj -
That is a little bit tricky because you can't see the API names from within the Marketo User Profile view. However, I did think of this during my test and chose fields carefully. E.g., there is only one "Company Name First Initial" field. There are two "Age" fields but one was already hidden from the Marketo Sync User and I hid the other one. The field I was manually changing in step 4 was "Twitter URL." There is no other lead field called "Twitter URL."
In case anyone was curious (or runs into a similar situation), I finally noticed that the Marketo Sync User was assigned the Sys Admin profile rather than the Marketo Sync User profile. So, of course, changes I was making to the Marketo Sync User profile had no effect. The solution was to fix the profile assignment.
We're looking at doing this ourselves too. Do you know if we have to modify both the field-level security and the object permissions?
Marketo currently has "View All" and "Modify All" permissions on Leads in our instance. I'm curious whether we need to revoke that in order to move forward with hiding fields.