Ferrous B. is correct about two stems giving the same effect. The first "control" stem I tried was an old Moto Ace with a rather large stack height and only one pinch bolt was making good contact with the fork steer-er tube. That must be why it had the same feeling of looseness and movement as the stem with the cracks, (closer examination of the cracked stem revealed a hairline crack at the other pinch bolt as well). I have since tried it with a proper 40 mm stack height stem while waiting for my new one to arrive and the headset/stem is adjusted correctly. It would not be right to expect Ritchey to warranty this stem, as I bought it (supposedly slightly used) at a local gear swap and it may have suffered from a heavy-handed install at some point, a drawback for using light-weight used parts. And to think I bombed down some gnarly Pisgah trails with that stem. . . . . whew!
Thanks everyone.