Product review (5 stars): Good fan replacement
I have been buying used sub zeros and find that the only thing that ever fails after 10 plus years is the condenser fan.  If you notice the center wall of the fridge is warm when you open the door, there is something wrong with your condenser fan.  On the older models it runs all the time.  It's easy to check.  Replacing the fan is a little tricky without pulling it out from the cabinet and removing the top cover.  You Need to remove the screws holding it to the bracket.

This fan is just as quiet and efficient as the stock one.