Hi,Welcome to Justanswer.
I am assuming that you have tried out other blank discs to rule out the issue of a bad disc.
Yeah. This indicates that the mac's disc burner is going bad. I would suggest you get a laser lens cleaner and running it.
They are easily available in the electronics section of walmart or you can get them from your nearest bestbuy store or any store that sells electronic dvd's.
If that doesn't work there is nothing else you can do to fix it. I am sorry to say this but you have to replace the disc burner.
You can get the internal disc burner replaced or if its too much effort get an external disc burner online .Something like http://www.amazon.com/Samsung-External-Optical-SE-S084C-RSBN/dp/B002C1BBU8
B.t.w the leaser lens cleaner should cost you around $8
Hope this clarifies your doubts.
Sure thing. Let me know how it goes.
Have a great sunday.
Sorry it didn't work out.
I have asked customer service to take a look. Thanks.