Summary: been bolted up slip it back on to the base and check that it is level Whe satisfied remove again and super glue the lego part that is touching the alloy Once done replace back on the axle You should end up with something like this The inside of the alloy should just be touching the micro switch levers which will push out the bumper and you should have no slop in the bumper
Image Dimensions: 446 x 334
Image originally found here.