How to clamp a brifter to the bar more securely if the clamp is already very tight?
More detail: After a small crash (no scratches on me, just a few on the bike), one Shimano Ultegra brifter was wobbling relative to the handlebar. I tightened the clamp bolt that attaches the brifter to the bar as much as I could, but the brifter was still wobbling. I undid the clamp, removing the brifter from the bar and saw that the clamp is a bit rusty, but looks intact. Retightened the clamp bolt as much as I could (the hex key broke), but the brifter is still wobbling on the bar. Before the crash, neither brifter wobbled.
There is no bar tape or anything stuck under the clamp or brifter edge, I checked before retightening.
The Shimano dealer manual does not give additional info besides tightening the clamp bolt (http://si.shimano.com/pdfs/dm/DM-ST0002-05-ENG.pdf).