Just a side note but the DAT cleaning tapes are only good for a certain number of uses and it is not apparent when it is used up, so it is important to mark off each use.
There is a build up which probably can not be removed by a cleaning tape. About the most you can try is to load the cleaning tape a few times in a row with the hope it will restore the drive to a functional level.
If that does get you full backup then for the first few times I would clean it again each day.
However if it does not return the drive's ability to perform a full backup without the need for cleaning then it is time to either have the drive serviced or replaced.
One more consideration is to look for environmental factors. If it gets too dusty, hot, or humid then it will also cause failures.
