If tires replaced and same issue, maybe have them check the halfshafts (rear axles) as some people have had issues there... otherwise the buyback may be the best bet.
Well, if I had any reason to pull a door panel I would check (no reason at this time). If I were to do it, I would have forescan at the ready, if there were no volts there with turn signal on, I would see if I could program it to work, while I had the door panel off.
Just put on the factory one... looks the best (centered), does not block the radar sensor, and actually does not make holes in the bumper (holes are in the grill).
Last summer I replaced tires on another car (cadillac not the S650) and had all kinds of vibration with the new tires. Rebalanced several times, replaced one tire that seemed the worst, still had vibrations... returned those tires for another brand tire... smooth as, well, a cadillac.
The top 2 choices for all seasons are Michelin Pilot sport all season 4 and Continental DWS06. I have the Michelins on my S650 and the Continentals on my S550. If you stay with the 19" diameter, width choices become limited. If you want max rubber, going with 20" diameter gives much more...
Looks like may be same plugs/pins used. Pins 1, 2 & 4 control mirror direction, 3 & 7 are turn signal + & - respectively. Time to pull the door panel and look...
If you are keeping stock springs you will be fine, lowering springs can increase the likelihood of tire rubbing... he was just saying that his size works even with the lowering springs.
Looking at the wiring diagrams; the cars with memory seats actually have driver's door and passenger door control modules... all of the wiring to the mirror comes from there. On cars without memory seats, all of the mirror wiring comes from the respective module; BCM for turn signals and puddle...