first of all an apology - I thought I had notification email set up, but I obviously didn't do it and missed your postings.
The Mediatek controller chip has the following codes:
The rubber pad on the spindle is very sticky. I will follow your advice and clean it (cotton but + isopropyl), but I doubt very much that any dvd slipping might have occurred. Occasionally I saw a disk "jolt" like starting to spin, the motor stopping immediately and the DVD go back to the preferred location (magnets realigning). Since then the motor seem to have packed up entirely, but there maybe another issue here. The first two tracks on the ribbon started to "peel". I trimmed the first 1mm of the ribbon with some very sharp scissors, but this may not be enough, as the tracks looked "squashed" (where the terminal contact originally sat), another 1mm or so. I did not want to cut exactly on the "squashed" tracks because the ribbon itself i sony "stiff" for a short length, once I cut it all it would become impossible to insert the ribbon.
I had a look at the SHM-165P6S pictures. Unfortunately the ribbon for the spindle motor is way too short to be suitable; also I cannot see the ribbon for the worm drive.
The SOHW-1633S also seem to have the same "short" ribbon (but a different Mediatek chip).
BTW, I did try to swap the lens and caddy assembly between the two drives. It did not work. the disks were never spun, it looked dead as a dodo. But when I put everything together as it was before, the unit worked for few days. I burned few DVD+RW, but again it was very inconsistent and failed few times at the end, while closing the recording. Since then (I tried to lubricate the worm drive and the caddy rods) it stopped working completely (DVD is not spun).
The other thing I noticed is that the open/closing of the tray is not as smooth as I remembered. So much so that few times I saw tray closing so sharply that dvd would move out of place and would not center on the spindle. Sometimes the tray would then re-open, BUT NOT ALWAYS (this would only be noticeable now, without the unit's cover). I tried to tighten the belt (by loosening the screws and moving the motor/pulley a little), and it might have been benefitted a little.