Just an update...
New bottle door gasket came in (thanks FunTronics!). Haven't had a chance to put it in yet. Will try this weekend.
Weather wise, we got back down into the 30's-40's. Had it plugged in yesterday, and condenser fan was not running constantly, and machine held temp around 36 degrees with thermo set at 2. It's supposed to be colder for a few days, so I will leave it plugged up to see if the condenser fan kicks on and off at regular intervals and holds temp like it should. More info to follow.
In the meantime, looking at the bottle door (or they call it, port gasket, part 7) per the schematic, it's held in place by being sandwiched between the main door (part 1) and the port assembly (part 37) and held in place under tension via machine screws. I am hoping that all I have to do to change it is unscrew, pull the old gasket out, shove the flanges of the new gasket back into said gap and re-screw? Or does it require the the back half of the door to be taken off completely, to get at the port assembly?