Try P2 (pericardium 2). Find it on the map at any of the PP charts in the links on a separate thread in this forum. Punch it straight in and in between the heads of the bicept muscle in the upper part of the upper arm. Take turns throwing hook punches to each other while the other person tries to punch this point. Go easy. It doesn't take much. When you get hit with it, you should feel a tingle right down to your fingers. In sparring, go harder and uke's hand will jerk up and away in pain leaving him undefended for a second unless he knows it is coming. Even if you know it is coming, the cumulative effect after a few good hits is to not want to strike with that arm again.
Try it and post back telling us how it went.
The older I get, the better I was!