Not completely certain about the part on the loader's hatch that you mention but it sounds like the mount or hasp for the padlock (used for locking the tank shut). Perhaps the factory workers got some glue on it by accident and glued it shut. It should open so you can turn the airsoft unit on and off.
Here's a pic of what I think you're speaking of:
http://tanxheaven.com/ljs/pershing1-16/40.JPG
If the hatch's handle is at 12 o'clock, the padlock hasp is 11 o'clock.
-Harq