Why does opening up an ISO file in some sort of "emulation mode" (whether you are opening it in VLC or mounting it in a virtual drive, it is emulating it as a mounted disc) be related to GPT? Are you changing subject here, I am confused again.
What are in those ISO images? Seriously, just keep the original media files (MP3/MP4/AVI/MKV/WMV/whatever). Now, if they are rips of DVDs/BDs then that's a different thing, but let's not go there.
As have been said, if you suspect the drive is failing, backup, and run the manufacturer's diagnostics. DVDShrink/VLC may well have bugs that lead you to believe that the drive has failed.
The Model M is not for the faint of heart. You either like them or hate them.
Gerbils unite! Fold for UnitedGerbilNation, team 2630.