Look for ice /frost in the freezer. If you have a frost buildup on the inside of the evap cover/panel it is much worse behind and blocking airflow. It may be not defrosting. I think these had a glass tube defroster with an element inside that is prone to failure.
If you see no ice buildup and the unit is barely cooling you may have a sealed system problem.
If you don't wish to disassemble it, unplug it for 48 hours to let ice melt. If it begins cooling normally again in 12 hours and is fully cool in 36 you have a defrost issue.