Unfortunately dust and scratches although not good are not the only problems.
A disk may be "Bad" and yet show no phsyical signs. A disk may well play and yet fail to copy because the process of copying is more demanding.
Do you know anyone with a Liteon ? I have found that files which can not be copied using a BenQ or a Plextor can be read by a liteon. It would certainly be worth while trying any other DVD drive.