Are you sure you have your hierarchy setup right with your transformations? {% MeganavDescription %}
should display the document being rendered data. For instance if you have:
-Home
--Products
---Prod1
---Prod2
---Prod3
If you were navigating to /Products/Prod2, it should render Prod1 description, Prod2 description, Prod3 description as each of the documents are being rendered in the navigation. If you simply want the current document you are navigating to, you'd use {% CurrentDocument.GetValue("MeganavDescription") |(identity)GlobalAdministrator%}
. Then you'd see Prod2 description, Prod2 description, Prod2 description.
If you were using ASCX transformation it would be the difference between <%# Eval("MeganavDescription") %>
and <%# CurrentDocument.GetValue("MeganavDescription") %>