> BTW what does self-cleaning mean? We have SL500 drives but the Sun
> (Storagetek) engineer has assigned a slot or 2 for cleaning tapes so
> they obviously consider the drives might need cleaning tapes, although
> they are supposed to be self-cleaning.

Tim, I ran across that while looking for details on drive compression.
I think the best writeup I found was on Overland's site and was on LTO3s
(make allowances for failing memory,  please).  

I was most surprised to find that the drive has its own little
nose-wiper which, when it senses the need, physically runs a little
cleaning pad or brush over the head, then retracts out of the way.  The
writeup went into some depth, including how it rejects any but the
correct cleaning tapes, how it rejects even the correct cleaning tape if
the drive doesn't think it needs to be cleaned, and how the primary
cleaning mechanism was the drive built-in wiper, not a cleaning tape.
All this effort to avoid cleaning when not necessary reflects what
someone pointed out early in this thread--cleaning tapes are unburnished
tape, hence more abrasive to get the crud off, but once the crud is
gone, the abrasives start removing head material.

In the olden days (reel-to-reel, "real" tape drives), 91% isopropyl
alcohol and a Q-tip, cloth, foam pad or tubegauze worked just fine for
tape and disk heads.  :-)