Did the same on my xc bike, went through loads of qr's tightening them up till they broke. Could grind some slots in the drop-outs so the qr as something to grip on to? Or get a good size washer, make some dents in it by hammering a blunt nail in to it on both sides, trying not to make holes in it and put that in between the qr and dropout? Again to give the qr something to grip on too. It's a total bodge but it's not budged one bit since I did it on my bike. slots... er` that's not what you meant is it? :$ Mine is rounded off and slips out the dropout when I pedal hard.