Originally posted by UncleVanya I get a lot of emails on this topic and get contacted about this and monitor threads on this. Spontaneous recovery on SDM is real. It happens without a lot of clear repeatability. Sometimes it wakes back up and never seems to go back to sleep.
As for screw drive - Adam and I exchanged some posts about this. Yes screw drive can fail. I have only seen it fail on two lenses myself. In both cases the failure appears to be related to the lens communication module. Both lenses reverted to M type or K type function - loss of aperture automation, loss of autofocus was simultaneous. One of the lenses was dropped and damaged (fa 35) and the other was an FA 80-320 that has a number of complaints about similar failures.
Dropped and damaged = not a spontaneous failure.
80~320mm = earlier generation AF, and as you noted, has a history of problems.
So you've documented one spontaneous failure in a discontinued, early screw-drive AF lens. How many cases of non-screw drive AF failure have been reported? My general impression is that screw drive became close to 100% reliable, if slower and noisier, but non-screw AF is erratically unpredictable and many - possibly - probably most failures are spontaneous, not a consequence of physical trauma to the lens or camera. I find that discouraging and annoying. I could have paid $360 for a repair that happened spontaneously as soon as they tested the lens.