Hopefully Gene can help me out here, I posted another question under the "freezer fine, fridge not cold" sticky tab. But that was before I developed my Hypothesis.
Quick run down and hypothesis:
Old Gibson "frost clear" fridge, freezer on top, freezer fine, food compartment too warm.
Took apart and found an Ice dam in the drain trough covering the drain hole.
Defrosted unit with a hair dryer, reassembled, restarted cooled fine for a month. then got warm again. Took apart and exactly the same issue, this time I noticed a foil wrap around trough with wires, A trough heater. I am assuming a bad one at that. all other defrost components seem to be fine.
Heres the hypothesis. Please interject if I am wrong.
The cold air funnels through an unobstructed(no damper) passage from beside the coils down to the food compartment. There is no venting other then the evaporater drain which actually goes through the refrigerator compartment ceiling directly into a drain cup and out the back. My theory is that when this drain hole plugs with ice, the cold air has no way to circulate into the food compartment, Unless the obvious(fridge door is open). With the drain clear and unobstructed, the food compartment chills like mad.

Now with the problem explained. Is the trough heater itself all to blame?
Or is there a possibility of something else like defrost thermostat?
I am assuming parts for this old girl are going to be tough if not impossible to find, but I would sure like to try something as this fridge is an odd size and fits just perfectly where it is and has always run so cheaply and well.

One fix I read from one of your volunteer techs, is that to extend a piece of #12 bare copper wire into the drain hole thats wrapped to the bare copper coil heater above. It was said that this works well. What say you about that for a quick cheap fix? Or on the other hand is there a universal heater of some sort I could install in place of the old foil trough heater?
Thanks in advance
David