DVD drive does not play some DVDs properly

Question

Hi,
My Macbook was purchased in 2007; So it is a bit old. I haven't used the DVD drive very often.
I bought two new DVDs from Amazon recently. However, when I played them in my Macbook using DVD Player, the disk pauses and skips very often, making it impossible to watch the DVD. In addition, the Player would display the "Skip over damaged data" warning.
I thought it was a problem with the software (DVD Player); so I installed the VLC player. Problems occurred as well. Disk would pause and then simply stop (the screen closes).
I thought that perhaps it was the problem with the Amazon DVD disk. So I played some other DVDs in my Macbook, with both DVD Player and VLC Player. There was NO problem at all with the other DVDs.
Then my conclusion was that the Amazon DVD was faulty. I requested a replacement, which they sent to me promptly within a day.
However, the same problem occured. The replacement DVD would not play properly in either DVD Player or VLC Player in my Macbook. It would pause and skip very frequenntly.
Now I began to suspect that maybe the Optical Drive was faulty. So I brought the DVD to my school and tried to play it in two computers: one PC (with VLC); the other Mac (DVD Player). To my surprise, the DVD played flawlessly in those two computers.
Now my conclusion is that the optical drive of my Macbook is faulty.
However, after doing some preliminary research on the internet, I find that replacing the internal optical drive is a difficult process. The alternative seems to be buying an external drive. But there seems to be concern about booting the computer (when the need arises) from an external optical drive.
Questions:
1. Is my conclusion justified? (That I have a faulty optical DVD drive)
2. If the optical drive is faulty, then why do some DVDs play with no problem in my Macbook?
3. Would you recommend replacing the internal drive or puchasing an external optical drive? What are the advantages and disadvantages to both?
Thanks a lot!

Answer 1

Thanks again. I went ahead and deleted the DVD Player folder and the plist file.
The result is that it appeared to temporarily improve the playback of the DVD. For the first two hours, the DVD paused considerably less and each pause was of a relatively short duration. There was much less skipping. So the playback was almost tolerable, if I lower my standards.
However, after two hours, it reverted to its old ways. The pauses and skipping became so frequent and long (as before) to make the DVD simply unwatchable.
I don't know what to make of this.