I have a pocket door, about 3 feet wide, solid door (heavy) which hangs from a metal track at the top with two rollers. The door is not sliding easily and keeps coming off of the track. It has worsened. Now, the problem is it appears that the rear roller has fallen off of the track. That roller is in the wall. What would you suggest, short of opening up the wall, to solve this problem? I would truly appreciate your help. Thanks.