From the BenQ FAQ sticky:
Q: Do I need to flash B7L9 first before switching to another firmware version?
A: Possibly not between firmware flashes but if your results are not as good as you would have expected, then try flashing back to B7L9, power off, and then returning to your current firmware. It could make a difference.
Just, FYI ... flashing to B7L9 and rebooting 2x between firmware upgrades actually improved my burn quality. I don't exactly understand how / why this helps, but I just know i get much better results this way. ( I typically switch between B7U9 and B7V9 because of different media doing better with certain firmwares ... a pain, but worth the better scans ).
Good luck with your burner. Hope you get it squared away.
Also, a quick note ... you may want to examine the burning surface of your blanks before you burn (and the drive tray as well). Any large particles / dust can contribute. I once had a small little crumb of a peanut in my drive tray somehow. And, I thought my drive was going dead because I was getting HUGE PIE/PIF counts. After, dusting off thoroughly with compressed air, everything was fine. << looks for wood to knock on >>