This is a fan with a plastic cap that is eroding. Almost all fans that are sold now are made with metal caps.
This fan not only has a plastic cap, but the part that goes under the shingles and extends vertically is plastic as well. Note the vertical crack that is causing a water leak into the attic along with the fact that part of the cap has eroded away.
Shown below is a new fan complete with automatic thermostat which I normally set between 90 and 100 degrees. All metal construction.
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