Servo horn's screw is backing out...

Nice tires too. Now if you can manage to make it 4wd again, your tire problem will probably ease up, and you'll have monstrous amounts of traction.

I like the simplicity of the setup. Have you considered doing direct diff for the front as well? A guy over at RC zone (GordonFreeman username) did a direct to diff setup for both the front and rear of his buggy. The only catch is you need two ESCs and two batteries.