(3) The cracks around the motor solder pins are a little more common than "a few others" because the motor's weight is supported by those pins being soldered, and once you remove the two frame screws, that's all that's keeping it on the board. The solder has become brittle over the years, and if you have any history with all the electronic relays in this car, you know the solder cracks around the heavy parts. And now you're handling it.
This reflow being recommended often divides the failures from successes because care must be taken to keep from loosening the motor pins in the plastic bobbin or damaging the motor winding termination on them. That means reflowing the joint quickly - say one second - with just a touch of new resin flux core solder. These joints are tin/lead solder, not the stuff you can buy today at Walmart.
adding my own experience: re-flowing those two cracked solder pieces fixed the random intermittent odometer issue i was having. did a quick lap around the neighborhood and it worked perfectly the whole time. i'll update again if it fails again.