I saw on a Schumacher US drivers page they are using B4 caster blocks with B4 hex front spindles. to modify the caster blocks, they will sleeve the hinge pin hole with brass tubing. I was thinking this "sleeve" could be used for the B4 rear aluminum hubs. ream out the hinge pin hole and insert a sleeve with the internal diameter to match the hinge pin (1/8" ?) this could address the slop issue.