One last follow-up. The science experiment is complete. Aluminum stem is gone. Steel and chrome are unharmed. I washed the fork down thoroughly with water and then sprayed every inch of it with WD-40 both inside and out. "Sanded" the chrome with a wad of tin-foil and the foil/WD-40 combo took off whatever rust there was on the chrome. Beautiful, clean, ready to re-install once I find a new headset.
This sliver of stem is all that was left in the fork when I took it out of the bath. Had I left it a little longer, even this would have been gone.
