I just found an extremely in-depth website for those, like myself, who find it crazy that CD/DVD drives don't seem to last more than just a couple of years (when I still have electronics built in the 1960s that still work fine):Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives (Also largely relevant for DVD/HD DVD/Blu-ray equipment)
In it, the author states:
"Many common problems with CD players can be corrected without the need for the service manual or the use of sophisticated test equipment...
Mechanical - dirt, lubrication, wear, deteriorated rubber parts, dirty/bad limit switches, physical damage. A dirty lens (coated with dust, tobacco smoke residue, or condensed cooking grease) - easily remedied - is probably the number one cause of many common problems: discs not being recognized, seek failure, audible noise, and erratic tracking, sticking, or skipping.
Even many professionals may mistake (either accidentally or on purpose) these symptoms being due to much more serious (and expensive) faults. Don't be fooled!"
The author provides very impressive and comprehensive information on symptoms, troubleshooting steps and maintenance and repair steps... and very good advice every step of the way. On the issue of lens cleaning, he has little faith in optical drive lens cleaning discs. And these discs do not clean the mirror.
And, now that I have two internal optical drives (in my old G4 MDD) that no longer recognize discs, I will attempt to bring them back to life before I attempt it on my just recently replaced external drive. After reading from this guy's website, much dust is suspected in all cases.
If an optical drive is dead, it's dead. But if correctly cleaning a couple of components could easily restore it, I'm game.