Fridge keept building up ice in defrost drain drain in freezer. Once the drain pan filled with ice it drips into fridge compartment. After taking things apart three times to thaw it out, decided to replace defrost components - heater and temperature switch. In addition to new parts, also added a 12 gauge copper wire hook that hangs from defrost heater into the defrost drain.
After this, the defrost cycle is running as expected, but will not know if the issue is corrected until a year or so goes by. Hope this fixes it.
The repair took about 4 hours because had to empty/load fridge, melt all the ice, and put in new parts. If you only count the time to replace parts, it took about an hour.