As I recall, you made some modifications to your wind sensor assembly. Is it possible that you did something to crack the top?
Nope. This is the one that came with the new fan that I got from warranty. All I did was take it off and put it on the broken dual fan and set it on a table outside as another wind speed reference. Today, it was very windy, and I notice the spoons not turning well. I look at the top and see it has developed cracks... I pull it off and water is down in there. Now the original one that I modified, already had cracks in it and I had sealed it up a long time ago. I had never taken it off the bearing and it had cracks. It would stick in cold weather and now I know why. Frozen water.