Good for you, the fans would appear to be somewhat biodegradable!!! I have just managed to refurbish mine, looks pretty good now, for a little while at least.
The fan motor is pretty well shielded from the weather, but the steel case and brackets that go on the back of the radiator seem to corrode really fast - I suspect the warm air/water from front wheel combination is not a good start...
They look a lot better after a good coat of paint, but this only every seems to be a temporary solution!