Cleaning the heads is more dependent upon the quality of the tapes than anything else. At this point, I would use a "WET" cleaner if available. You take the chance of disturbing what little dirt that is there as well. Be careful. If you have any doubt, remove the unit from the vehicle and have a pro clean it. There is a good chance that the belts are nearing their end of life too. These can be changed and the pinch roller can be treated to get it back to normal too.

Dan