One would presume that the fan motors are lugging under too much drag. This will reduce their back-emf to the point that the heaters are toasty.
It is high time to convert this system over to intelligent, variable speed cooling fan motors. The economics are overwhelmingly favorable.
It doen't matter if you can reuse the motors or anything else. In economic terms they're worthless; kind of like a 12 year old personal computer.
Don't repair it. Replace it.
