I didn't repair anything... but I did decide to UNrepair a flaky HDD!
Exhibit A: one worn-out 500GB HDD with lots of bad sectors
Hey, I found the "void your warranty" screw! (This drive's warranty ran out years ago, so I don't care)
Look, ma! No head unload ramp! (I thought all semi-recent drives had one, but this one apparently still parked the heads on the platter)
Platter retaining ring and head actuator have been unscrewed...
Barracuda 7200.10 500GB, exploded view
I was unsuccessful in my attempts at harvesting the head actuator magnets. They were stuck to the brackets surrounding the head actuator pivot with some pretty strong adhesive, and my attempt to wrench them loose just broke them into pieces.