1. Servicing - You will have to examine the optics for cleanliness, they come out on the tray in that type of Optical Drive, A LED torch and magnifying glass for that. Once a year job for my old Laptop.
2. Test software - Do Write and Read tests to determine what actual speeds you are getting, a few large files rather than numerous small ones which will be much slower.
Compare that to the specs of the Optical Media. The DVD drive itself likely to have specified speeds much greater than easily obtainable Optical Media.
3. Test Media - New Optical Media, I would suggest CD-RW and DVD+RW.
Optical Media deteriorates with age so you need reasonable new stocks.
The Apps I use for Testing are VSO Inspector, and an old version of NeroDiscSpeed, both rather old and the latter is run in compatibility mode for Windows 7.
You can of course devise your own Write/Read tests with large files.
