The main issue now seems to be that the ceiling of the refrigerator compartment is full of water that leaks into the refrigerator. I thought I'd had this fixed last week (by pouring lots of very hot water into the freezer), but evidently not. For several days, the pan under the refrigerator had water in it (I emptied it at first when it was very full, but then the volume tapered off), so the tube had definitely been opened at least briefly.
How do I access the drain tube in this thing? At the rear of the refrigerator compartment, I can see a tubular housing going from the freezer floor to the back of the refrigerator, clearly housing the tube. But I have no idea how to get to the tube itself, or to the pan under the freezer floor.
My now-secondary question is what the cause is of a good amount of ice that has built up in the freezer. It's just at the front edge of the freezer opening, so I am suspecting that maybe it's the gasket. But I can't feel any air escaping from the freezer when I hold my hand there.
Five days ago, or so, I vacuumed the coils under the refrigerator. They were a mess and may not have ever been vacuumed. I'd hoped this would increase performance and prevent the ice build-up, but it's still there.