Mac Pro DVD Drive Weirdness

Here's my problem:

I have a Mac Pro (Dual-Core), and the DVD drive is becoming increasingly flaky. Any DVD Video I burn from the internal drive from DVD Studio Pro projects to client MP4 files (I use either Toast Titanium 8 or 10) will play on any other computer (Windows or Mac) and even on cheap set-top DVD players, but won't play back on my drive. Mass-produced DVD, CD, and even CD-R media work fine. I've been using DVD+R media for about 3 years with no issues before now.

I've cleaned the lens with a Q-tip and 99% isopropyl alcohol, I've reset all the connections, tried different media (including Taiyo Yuden) and different burn speeds, and all I get is either "blank disc" or "Unreadable Disc" dialogs when I insert the disc after burning. Did I mention that this is pretty embarassing in front of clients?

So, before I use my drive for target practice, I'd like to know if anyone can recommend any kind of process that might be causing this (repairing permissions, trashing prefs, etc.). If the drive is end-of-life, fine--I just want to know one way or the other.

As usual, thanks in advance for any and all helpful info...

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