I visited some folks this weekend who live back up in the hills in a northern county. He was doing a foundation repair on his house.

The old foumdation was shallow, un-reinforced with steel, and cracked.

The room involved was a nonconforming low-ceilinged room, with wood floors with lots of earth contact and a musty odor of rotting wood.

My friends solution was to excavate inside the cracked foundation 12" below the bottom 

of the old foundation, undermine it by 2", form & pour a new 6"x 24" concrete footing the length of the room. ~9'

One day at a time, the insulation on the wires to the motor got softer and oilier.

Over the years it broke down gradually until one day, the voltage began shorting to the motor housing.

Slowly and imperciptably at first perhaps, but finally and suddenly,

the motor overheated. The fan belt was not well aligned with the motor shaft either, adding heat and wear to the system.

A new motor purchased at Grainger was swapped in and realigned with squirrel cage fan.