Welcome Mr. Stickler,
The troubleshooters among us may point to an air flap or something that might be stuck somehow, or blocked by ice, or who knows what. If the freezer temp isn't dropping too, then it may in fact be something other than the cold control, since trying different ones made no difference.
My mom's '75 Coldspot side-by-side was still running when it was sold in 2008, and all it ever needed was a new condenser fan motor, and later a new relay -- both simple repairs made by me. I hope you can continue to enjoy your rare, beautiful and well-made refrigerator for years to come.