Straightening them would be my first thought, they're made of pretty malleable stuff.
Might be teaching Grandma to suck eggs here so apologies if I am:
Not tightening up could also be the rubbers spinning inside the bars if you've loosened them a bit too much and now the rubbers won't grab.
Might be worth removing the entire bar end assembly (taking care not to loosen the screw so far that you leave the rubbers and lock nut up inside the bars). Tighten them slightly out of the bars so it takes a bit of a wiggle to get the partially compressed bungs inserted into the bars, that way they're pre-squeezed and should tighten properly.
Failing all this, I would be very surprised if the screw in question wasn't the same 6x140mm screw used in late year generation 1 DL1000s which came with knuckle covers as standard. Every other part in the handlebar balancer assembly is the same from 2010 DL1000 to 2014 DL650A.
https://www.fowlersparts.co.uk/parts/view/09127-06023?noredir=1
