IMHO, if you have cracks at the fan blade & hub, replace the fan. It is just a matter of time as to when that fan will fail, the blade(s) separates from the hub.
Actually the white plastic cooling fans that always crack like this within a year or 2 or 3 are the cheapo replacement aftermarket ones made in China that AutoZone, O'Reilly's, Schucks, Pep Boy's, and eBay and Dorman etc. sell. Dorman used to be made in the USA, but no more-- as you all might know mostly manufactured in China.
I know this for a fact because I bought one of those cheapo replacement fans for my 94' OHV V6 and after 2 years, when I was going to change the serpentine belt I saw the big stress cracks all over the hub at the blade, as in the picture in this post. I could not believe it. I took a made in 1995 MY fan part, OEM Ford with the dates of manufacture cast into the part, from my 96 Explorer, with 170k miles, that was having the trannie rebuilt and THAT fan blade was fine. No stress cracks after 16 years of hard running and installed that in my 94.
I then ordered a new OEM Ford plastic fan blade from a Ford dealer in Buelleton, Calif. for my 96 Explorer and with shipping it was about $8 more expensive than the cheapo ones from AutoZone, etc.
The OEM Ford manufactured fans last much longer- And most of the older Explorers like mine, 1996 OHV V6 run much better with oem Ford / Motorcraft parts. I have owned 5 or 6 of these trucks over the last 15 years, all high mileage, do my own repairs and that's what works on them.
Unbelievable how bad the quality of the aftermarket parts are that are now being sold by AutoZone, etc., even with their " warranty ". Their crappy parts all fail within 2 years... I've started buying only OEM Ford / Motorcraft parts for my Explorers.