is my sony dru 500 ax wore out ?

here is my question , i have a sony dru 500 ax burner . ive had it for a year and a half now and used it alot . its been working good until yesterday when trying to back up the passion of the christ .
ive been using 4x media for a while now with no problems . ritek ridata go4 is the media im using . yesterday it would not burn at 4x and kept coming up with a error when trying to burn at 4x . i have cleaned the drive , made sure the firmware is up to date and made sure its in dma mode and also tried different media . it will not burn over 2x anymore . i looked in the event viewer in xp for the error it is having and it says , device cdrom has a bad block . what does this mean ? is the drive finally wore out ? i use nero 6 ultra and clonedvd2 for all of my backups and neither program will no longer burn at 4x like they used to . ive tried about everything i could think of to get the drive to work again at 4x . my burning software is also up to date . i even tried reflashing the firmware and it is a no go . what i mean is it has a error now when trying to update the firmware . nero doesnt even show it as being able to burn at 4x any more like it used to . im thinking the drive is on its last leg as it has been used a real lot . im just wondering if any body else has a opinion on this that might help . thanks