I don't mind so much that it doesn't lock, but (on mine amyway) the chest "floats" above the bottom of its range of travel. If you press and release the chest, it will flex downward and rebound back up slightly.
The problem lies in the gray crosspiece on his back, just below the hinge for the chest. The internal gearing for the head auto-morph (a pair of curved "racks") hits the inner surface of that crosspiece. My solution: cut away the spots of that crosspiece that the gears hit. I used a drill bit, drilling a hole carefully into the piece. Done right, you'll see the ends of the gearing. Use a pointy blade to square up those new holes, and you'll see the gearing come back into those holes slightly, just enough to let the chest reach its full downward position and stay there. It actually helps his head rotate up a teeny bit more, and lowers the chest that much.
I'll post some pics, feel free to remind me. And not 30 seconds from now, either, wise guys.
