Whirlpool WRF736SDAM13 Gold Series Refrigerator Defroster Heater Assembly Part Number 12729123
The coils are getting covered with ice and frost in the freezer section, so tested the heater defroster and it is now working.
The best deal I could find on the part was at GRP for $58 (there were a couple of other places for around $44). I have ordered with Genuine Replacement Parts before and they are reliable, so I am using them. https://www.genuinereplacementparts.com/12729123-oem?gclid=Cj0KCQiAosmPBhCPARIsAHOen-MwnMYLJMhXkh-sKt20pjue8K67F7chAVgybI713Lim11sJ6OXb1wwaAsEiEALw_wcB
Repair Clinic price is $96.
Kitchen Aid and some other sites sell it for $113.