Absorption fridges do not like to be not level when on. The tubing you see in the rear flows both liquid and gas first to the freezer and then the fridge. Unlevel can cause the anti-corrosive powder present in the liquid to cake at the tight turns and transitions. Driving them down the road is helpful as it causes mixing of the liquid.
Typically when the freezer is good and the fridge is not then it is the beginning of the end. As long as you have good air flow across the back, propane flame or electrical heating elements working it should cool to 32 degrees when you don't open the door for say a day.
Door leaks and thermistor position can cause problems but are easily remedied but the age of yours I would believe the seals should be good.
There is a place in Arkansas that supplied rebuilt units (with trade) and he is very helpful on these unit. Can't remember his name.... replaced one about 10 years ago in a unit that I had.
Good luck.
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