I have the same problem, with the same model optical drive (HL-DT-ST DVDRW GSA-S10N), and have done some research. It seems to stem from the fact that our (non-unibody, non-pro, plastic) macbooks are poorly engineered, from the casing point of view. They crack at the palm rest, sometimes also around the edges of the display, and have this optical drive opening weakness problem.
With mine, I noticed that the drive itself is ok, since it works just fine when the machine is powered on while open. And, oddly enough, even when I insert the CD or DVD through the external case plastic opening. As soon as I screw it closed, the problem reappears, and some CDs/DVDs get scratched once in a while. I've tried to close the case with the screws a bit loose, but this didn't work.
Looks like the drive itself is ok, but we have to somehow unbend the case at some specific spot which isn't clear to me exactly where.
If someone would be kind enough to enlighten us, please do so.