Originally Posted by Andy_K

I'll offer a rather unconventional method that I stumbled upon once. I recommend this only after trying the conventional tricks, but before resorting to destructive methods. The technique: leave the bolt loose and ride it. You can see the thought process that led me to this method (except that the loose bolt part was accidental). I gave up on a stem and just decided to ride the bike as it was. Then one day while I was out riding I noticed that the bars were not aligned anymore! I think the relevant effect is that you get thousands and thousands of micro-impacts and eventually it works itself loose. Chip seal would probably help. Proceed at your own risk, of course.