We have been having similar problems with our StorageTek L700 Library and
DLT7000 tape Drives.
The Stk engineers have replaced the drives, replaced the robot hand.

Now they say there was a manufacturing problem with the rubber belt that
drives the robot.
They put some white-out on the belt and on the cam wheel to see if it would
skip a tooth over time.
It did skip, getting the two white lines out of sync.

The Stk engineers now say that corporate wants them to change the whole
robot instead of just the belt.
????
I'm waiting on the airfreight system in the U.S. to get this to me.

You can read similar problem reports in the responses when  I first
submitted this to the Veritas BU list on 7/23

Good Luck,
Brent

Brent Rohloff
UNIX Admin
CSC at Sikorsky Aircraft
203-386-4963
brohloff.csc AT sikorsky DOT com