Hi Edward,
This is also where I am having trouble. When I am looking at leads, I don't have a MSI option (that I belive you are referring to). I went to the admin section and tried to add it to the page layout but it was not an option for leads.
It was available for contacts. Below is what it looks like in the page layout.
When I click for more details, I get a different error. Below is an image of what I am seeing.
So I am confused as to why or where I can add a lead to a watch list and also why there is an error when I click on the MSI in a contact's view.
Thank you so much for taking the time to help me!