The roller assembly should be easy to remove. Simply remove the shell from the frame, and look for a screw close to the motor that has at least one wire terminal tightened under it. This screw goes through the truck and threads into the roller assembly. Simply unscrew this screw and the roller assembly will come right off. Don't lose any insulating plates or washers in the process.
Then see if some light bending on the roller assembly with a pair of needle-nose pliers or two can get it looking like the other roller. Or get a new roller assembly. Or, if you'd rather not mess around whatsoever with the roller assembly, cut a couple pieces of plastic to epoxy into the gaps on the switches, so the roller will ride over the gap instead of falling into it. Make sure the plastic spacer doesn't interfere with the movable switch rails.
