DAT72 drives

Hi all
I have two DAT72 SCSI tape drives attached to two individual servers (ser2003 &ser2003).
These drives do daily backup for about 5 hrs daily.
some times the backup just crashes in between and when I come in the morning I find the tape’s “tape clean” light blinking.
I clean drives daily.
Can any body suggest me what could be the problem.
is there any time length (age) we should use tape drive for, if yes how to know if my tape drive is dying.
Any one with any idea please suggest.
Thanks