Just a post that might save some of you some money. Had my rear mighty mite fan quit recently, so I ordered a set of replacements. Went to install replacement and found fan blades were jammed by a rubber O-ring, that's used to hold fan in place. Took O-ring out and fan works fine.
I plan to leave out the O-ring as I think it will jam blades again, but if anyone knows for sure that I should replace it, please let me know.