I still don't think the other drive was defective neccessarily, but it DOES sound like it was a quality variation issue.
remember, BenQ can only scan for certain types of errors, and I've had (and even posted) scans of media that looked great, but were completely unplayable in my PX-712a (which isn't a BAD reader).
Of course, the way drives are being made these days, if you keep returning and replacing them, eventually I'm sure you'll find one that works
That was true with the PX-712a and PX-716a, and also the NEC 2500a
Punch Cards -> Paper Tape -> Tape Drive -> 8" Floppy Diskette -> 5 1/4" Floppy Diskette -> 3 1/2" "Flippy" Diskette -> CD-R -> DVD±R -> BD-R
The Progression of Computer Media