Well, cleaning muck off the rails actually.

Recently bought an Eastsound E5 CD player which I was very pleased with apart from one little niggle which I sorted out yesterday.

It would start skipping on tracks 7, 8 (predominantly) and sometimes 9, yet play all the other tracks with no problems. Because it was only these 3 tracks on all CDs it had to be a laser carriage guide rail problem with either muck on it or lack of lubrication. The two metal rods are hidden away well beneath the loading mechanism and only just visible. I didn't relish the idea of hauling the entire mech out, so luckily my tin of spray cleaner has a long thin tube so a quick burst and repeatedly sending the carriage from the first to the last tracks did the trick. I used silicone lubricant afterwards because it doesn't seem to attract dust and hair like oils do.

This will often happen too with CDs that have many tracks on them because over time during "normal" use the laser carriage pushes all the muck and congealed oil to where most CDs that end at track 12 or so, then you find tracks 13 onwards skip when you bung in a long playing CD with many tracks.