Changing the thermistor isn't a difficult job once you find where they hid it. Usually just needs a couple wires to be crimped. It's emptying the fridge, and disassembling to find the location that's a pain. A repair manual for your specific model would help a lot. I'd only bother replacing if there's something wrong with the compressor/refrigerant, or you want a different model.

Is it possible to nearly soundproof (STC 60) bedrooms of 5-bedroom older 1920s house?

I saw a video of soundproofing with fireproof/resistant drywall, green glue and a second wall... but it was off a single wall in a basement--not a bunch of rooms next to each other with doors.

@BMitch - Already bought. $2000. Just spent some time pulling it out and ripping out the moulding on both sides to be sure the new one will fit. There are times it's better to drop $2K than to fix it, only to have it fail again in s few months. So far no food lost here, and new one coming tomorrow.