I have not heard of a lot of bad batches of dual layer verbatim media but it is always possible. Its more likley that your drive does in fact not like the media. You may or may not be able to fix this by trying diffrent firmwares. It might also be a very good idea to consider running omnipatcher on your firmware and apply the recomended tweaks.
Of course modifying firmware will void your warranty and Its not my fault if it kills your drive and the normal disclaimers.
Again, it may or may not fix your problem with this media. You might have to do a little playing with the firmware of a new drive to get it to work well with a particular media too though.
I wouldn’t nesasarilly consider your drive a bad drive. Its a bit old so maybe a new drive would compliment it and allow use of a broader range of media. I think I would defanatlly keep it for scanning and perhaps burning of some 4x/8x media if you have any. I still ocationally burn with mine (I have some old 4x media that burns beter at 8x on this drive than most drive/media combinations).
Fyi here also is an example of how the graph tells more than the data.
Drive: LITE-ON DVDRW SOHW-832S
Disc: DVD+R DL (MKM 001)
Selected speed: 4 X
PO failures: n/a
Elapsed time: 25:25
Number of samples: 231435
Average scanning interval: 1.09 ECC
Glitches removed: 0
From this information. you cannot tell if there is a large area of pif that goes up to 7 that will defanatlly cause problems, or just a single spike that may or may not cause problems. When you look at the graph, you see that there are just a few single spikes that go over 4, so they may or may not cause problems, so you do a transfer rate test to help see if those spikes will cause problems. The transfer rate test is nice and smooth, so the spikes most liklly won’t cause problems. This is an mkm001 burned about 10 months ago (I just scanned it now), most liklly burned on my nec 3500.