We have a built-in Sub-Zero fridge, which was installed by the prior owner in 1992. We bought the house in 2004. This is a fridge only, no freezer. Starting about 2008, every 3-4 months, it would form a large ice ball on the back wall of the inside compartment about half way up. It also wasn't cooling very well, running very hard to maintain ~42 degrees.
We called an authorized Sub-Zero tech who diagnosed the problem as a small freon leak in the coils, which was common for that model and age. He added some freon, charged us $150, and that solved the problem for 2-3 years. After the third time doing this, we finally agreed to replace the entire coils system with an upgraded part that is less prone to leaks. This repair was $800. It's now like a brand new fridge, even though it's 28 years old. I expect we'll get another 20 years.
We've had no other issues with it except a switch went bad that turns the light on when the door is opened. I changed it myself with a $14 part from Amazon. I vacuum the condenser fins about every 6 months and I clear the drain every year or as needed.
Not sure I would ever buy a Sub-Zero. But this thing is built like a tank. Since it came with the house and since it's built-in, we are more-or-less committed to keeping it running. We have a separate upright freezer and a separate built-in ice maker (under-counter).
We went through 3 refrigerators at our prior house over the 19 years we lived there.
That is just awful. I'd be furious. No matter what you buy, I hope it lasts at least 15-20 years.
