Michael,
first make sure you use the most recent plugin (v320r1) available here:
http://www.xsquawkbox.net/scenery/tools.php
if you use the very file you posted, put it into a new folder on your desktop, open the file in AC3D, export it to x-plane 8 obj format, will it still write the cockpit region data?
I have the gut feeling you are using a pre-release version of the plugin.
There have been quite a few changes in the way cockpit panel textures are recognized during the beta run.
cheers
peter