If a 5mm bolt is a loose fit then tap it to 6mm, since it's already about the right size for a 6mm tap. That'll help a bit. Is there any play in the adjustable legs where the lock screws fit? Maybe also check the holes where the lock screws go through to the bottom legs to see if they aren't flogged out too. The other thing that might be worth trying is some different top struts. To me, from an engineering perspective, the top struts look pretty close together where they mount on the rack. It might be possible reverse the mounting clamps on the struts so they're further apart and then straighten the struts to fit on the mounts on the bike.