Sometimes you've got to give it a light tap once you've got a little tension on the bolt, should pop right off.
I would bet that 50% of the bikes on the road with a original fan have these cracks. When one is advising others as what to do, sometimes we just play it safe. Then if your new one goes, we don't get the blame.
So, should you replace it or not? This is what I would do, not necessarily the wisest course. I would screw the removal stud back in the fan and mount the bolt with it's head in a vise. Then try rocking the fan while observing the cracks. If you see any movement of the cracks, I would replace the fan. If you don't see any crack opening or closing, I would mix some thin industrial epoxy and flow that into the cracks. Let it set up and then keep a ear open for strange noises or vibration around the radiator.
I had a fan a couple of years ago that I could actually flex the center hub in the fan. I did the epoxy fix and made sure it flowed completely around the hub. Two years later, and probably 5000 miles, I have no problem with it. Your mileage may vary.