Mac OS X may be right, but you may not get your money back! New drives are not expensive any more, dvd rom $20, dvdrw $30? Even a decent one is the same price as a set of ink cartridges for your printer.
I now know you've been running Nero CD/DVD Speed to benchmark the drive. FYI to just post the test data, open the test html page, copy it all, paste in notepad to lose the pic, remove excess blank lines, copy and paste where you want it. To post large images some people have been using photobucket.com or similar services.
The inconsistency in speed is a concern. Are there other things happening on your pc that may affect the test?
What was the benchmark for an audio cd like?
While the performance may seem erratic, is it actually causing problems playing back and burning?
Starman*