Didn't have any Brasso (yes, I actually remember what that is!), or light-duty sandpaper (only the nasty stuff) lying around, or even some contact-cleaner, so I tried a "Scotch-Brite Heavy Duty Scour Pad", and that did the trick. The sliding door lock now responds again to the driver's-door lock-unlock button. Thanks!!!
Yet, if anyone has the pin-outs for the powered or non-powered sliding door's contactor pad, please feel free to share it. Thanks!