Have you tried using high quality media such as TY -R/+R discs in this burner? It might make all the difference.
I’ve heard that some burners can be very picky when it comes to certain brands and makes of blank DVD media. So it might be worth getting some TY discs and giving them a go. If you start to notice the spots again after completing a burn, then the burner needs replacing I’m afraid.
Like I said earlier, I had the same problem a few months back. I’ve dug out the thread for you. Have a good read through it: