Well, when you update any field's permission to read-only for Marketo's sync user - Marketo can only read the data and cannot make any updates essentially.
The question / concern / situation is kind of reverse here if I'm not wrong - it's not that the updates from Marketo are causing any issues, it's rather the updates from SFDC clearing out the fields is kind of a situation of concern here. This usually happens when the fields in the Marketo have read-only access (i.e., no access / permission to edit the field(s)), and upon updating the data by Marketo's sync user as per updates in Marketo to SFDC, SFDC does not take the update but rather returns a NULL value which eventually wipes the data off in the Marketo too. Or, if the Marketo's sync user has the apt permissions to write the data than there may be the case where in the field values in the SFDC may have been wiped off at its end which would then eventually sync back to Marketo wiping off the data in the Marketo too.
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In addition to the planner, you should setup Program Templates that are pre-built and clonable. Put them in a folder called 95. - Program Templates. Use Tokens to be able to churn out these fast by dropping in replacable areas quickly. There are some threads on program templates, but the essence is: Program Template - Whitepaper Download Form LP Email Autoresponse 01 - Registration/Autoresponder (send campaign) My Tokens - create Text and RichText tokens that you will place into the Email and LP and will be in the same place, but have diff text every time.
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