You may have a simple fix .... I'll bet the lubricant on the rails that the laser sled rides on, has dried up, and is causing the laser sled to bind instead of moving freely along it's pathway.
When the laser binds and/or stops momentarily ... it losses lock with the data stream and it's ability to read the disc and skips until it can relock and read the data stream
Try cleaning and lubing up the rails that the laser sled rides on, and I'll bet that solves your problem