We have replaced 7 of 12 drives, with 2 more generating excessive cleaning requests. I expect them to be replaced within a few days.
The good news is that we rotate our tapes, so we are starting to re-use old tapes and should see this behavior stop. The bad news is that I have been assured that the tapes I am using are the "new and improved" reformulated tapes that should not be causing excessive head wear.
We have sent the last few drives to IBM for failure analysis, results expected in a few weeks.