The carriage rail of my Lettera 22 is not quite resting right on the rollers. It must have been dropped at some point, because the left side of the rail is not quite flush with the place where it screws in so when the rail rests on both the left and right roller, it causes more friction and it moves very sluggishly. Not sure how to fix it, because it doesn't want to stay where I put it. Any suggestions?