I recently assembled my MB and i have already ran into a few snags the main one being the coaster brakes, i had to bend the arm so that it would clear the frame and all was good so i was riding it for 3 days until i noticed one of the bolts on the rearwheel sprocket had fallen off, took a good look and noticed that the arm was getting eaten up by the bolts not only that but there was a ring around the sprocket where the arm had been rubbing on, so what do you guys think should i ditch the coaster brakes and get some caliper or disk brakes? what would be the fix for the arm rubbing on the sprocket?