I read the post regarding the L Fwd Entry Door posted a while back. Do I need to perform something similar in the XML file? Anyone else having this issue and/or know what the best way is to fix it?
Nobody ever reported this issue. The only reports were only about the L1 door, since apparently PMDG changed the configuration at some time, from using the standard Door1 variable, to a custom XML variable. But Cargo doors were always been custom XML variables, so the configuration that comes in GSX should work.
Of course, this assumes you are using the configuration that comes with GSX because, if you customized something you might have introduced the problem so, first be sure you are using the default configuration that comes with GSX, by pressing the "Reset" button in the airplane configuration page, and check if the cargo doors now are working.
Once you are sure they do, eventually apply the L1 fix discussed in the forum, and nothing else.