You know you can fit a new DVD-RW DL drive, it's quite simple, but if you've already installed Mac OS X as Dual-Boot it will nullify the installation if you don't fit the exact same model of drive, as when Mac OS X installs the OS it also installs the specific firmware for the DVD drive as well.

I bought a few spare drives for my own systems, for such eventualities in the future, as it seemed to make good sense.

The heads can often be cleaned with isopropyl alcohol and a very fine and very light (not heavy) piece of fabric - something lint-free, but if the disc or something else has 'scored'/marked the DVD reading/writing lens then it's probably useless - if you've got a good magnifying lens, like a jewellers eyepiece/loupe then you can usually see if it's beyond cleaning.

[ Edited by NewSense 14.07.2017 - 04:54 ]