Freezer & ice maker working great........OK
So the temps posted were from 'food section' (fridge is whole unit)
28*F then 40*F in food section??
Could be a bad thermistor (temp sensor in food section that controls overall operation of fridge)
Could be thermistor is in wrong position (brand/model helps determine where it should be)
Could be cooling unit is experiencing blockage (freezer section can be working properly but food section not due to blockage in cooling tubes between the 2 different cooling sections)
Unfortunately.......sounds more and more like cooling unit blockage given the age of fridge (1977)
Brand/Model........where the temps were taken.......how temps were taken??????