Over the past year I bought 4 PX755A. The oldest one (call it 1) died of natural causes 
a while back with power calibration error and refused to burn at all anymore. It was used a lot, so maybe no suprise there. It was dead, period. Easy to diagnose.
That drive (1) was exchanged for a new one (4) which still works very well and sits on the same power and IDE cable (slave) as the problematic drives, which you can read about below:
The first problematic 755A (2), jumpered as master on the same cable, was 2 months newer than (1), and developed strange behaviour about 2 months ago (give or take). It would always start the burn perfectly, burn well all the way up until the leadout. Then it would just start to click and basically take forever to finish the disc. In the end the pickup even hit the disc scratching it. I never recieved any error from Nero, and the discs were readable, but a Nero verify would give errors at the very last blocks. Plextools also gives 1-3 POF at the very last blocks. The amount burned didnāt matter.
Plextor sent out a new replacement (3) which worked perfectly for about 3 weeks (burning maybe 50 DVDs), an then, BAM! it started behave exactly like number (2). It burns perfectly all the way through up until leadout and then the clickety-clack starts.
Nero verify gives the exact same errors, and Plextools 1-3 POF at the very end, but NO errors from the burn itself. The overall errors with a full scan is quite good, with PIF at max 2, so the burn seems good.
4, the replacement for the first faulty 755A, still works perfectly on the same cables, and has done so for 200-300 DVDs.
I have used only Plextor DVD+R 16x and Verbatim TY 16x all the time (burned at 8x), so I have a hard time believing discs from the same batches all of a sudden goes bad. Especially since drive 4 still works perfectly.
Is it really possible to have 3 755A fail over a relatively short period of time? Two with the exact same fault?
The drives sit in a well cooled Antec P180 (with fan controller and 4 low rev 120mm fans with dustfilters), PSU is a Tagan 480W, AMD 4200+ X2, ATI X1800XT, 2 gig of Corsair 3500LL Pro, a Raptor and a couple of larger WD. No overlocking.
I have never seen any power related problems and Tagan is high quality in my experince, and I build computers for a living.
Firmwares used: 1.07 and Nero 7.9.6.0, but the problems started with an earlier version (7.2ā¦something). I think I used 1.06 in the beginning on drive (2).
If any of you have the slightest idea what could be going on, my gratitude will know no limits. 
) so itās around 28C, also in part due to the file server which is in the same room. But itās only 5C more than I have in the winter, but it could of course make things worse.