Since I started this thread a few days ago, I got another Lite-On (5007) [to circumvent macrovision]. The person who sold it to me stated in his ad that it's new, but I think it's used (the instruction manual looks like it's been read umpteen times) and no DVDs with the minus sign work in it.
Now that I think about it, regarding the other guy's post I was referring to a few days ago where he wrote that his Lite-On stopped being able to read a certain type of DVDs, they were -R's.
I found another broken Memorex DVD yesterday. That makes at least two out of a package of ten that broke not too long after I bought them.