The day crew was tripping in DP to 11,000 ft. The trip was stopped to visually inspect the fast line stabilizer guide which had been repaired the previous day. They observed it for 4 stands and found it to be OK. Later during the trip a loud noise was heard above the crew. The trip was stopped and crewmen searched for cause of the noise. It was discovered that the bottom outside roller of the line guide, weighing 6.5 lbs, had fallen from the stabilizer assembly onto the roof. It bounced to an unmanned deck and into a cargo basket. Both sides of the roller had visible wear. One side of the bolt thread was worn down and half of the other bolt was worn down due to roller movement after the lock nut had backed off. There were no injuries.