We had a cleaning problem with our 3590 Magstar a few months ago.  Here is
what we did though I don't know if yours is set up the same way.  We did
find out that the cleaning default 'preset' in the Library was not
initiating cleaning.  In the Magstar Library under Commands pull-down, then
Cleaning(first selection) is where we then set our cleaning schedule.
Select 'Clean based on usage', we set 100  where is says to 'Enter the
number of mounts before the drive clean operation'.  Under Maximum cleaner
usage; 100 is also set.  This has been working well for us.

Shannon Bach
Madison Gas & Electric Co.
Operations Analyst - Data Center Services
e-mail sbach AT mge DOT com