Quote Originally Posted by Jorpho View Post
What exactly could the problem be? Is it just dirt, or would I need a replacement part? (Obviously to attempt any repairs I would need to get those security screws out first.)
What kind of shape is it in? Does it look dirty?

The rubber pad inside there could be worn out, or it could just be years of dirt and finger gunk built up in there. Take a small toothbrush and dip in alcohol or warm water and work in and around the d-pad as best you can. Let it dry and see if that improves the responsiveness. If not, you'll have to take it apart and have a better look.