If you have the door still intact, keep it in place. It helps slightly in keeping dirt and dust out of the changer.

Now for the real deal. The lens/LED etc. rarely get dirty enough to cause problems, it's the mechanism. There are two horizontal rubber coated rollers that feed the cd into the "play" position and re-insert the cd back into the magazine. These are tacky and pick up alot of grunge from the cd's. When they get grungy, the cd will either fail to load properly or load into an occupied slot. Bad things.

If you can source some long "q-tips" use regular old rubbing alchohol or cleaning fluid and wipe these down from the mag entry slot.

If you can't get to them. Take it apart and get them clean. No problems after that. It's not a big teardown, just the metal covers.

Questions...reply and I'll go through the details.