I have a local craigslist add for a renissance i may go look at so i'd like to pick you brain about your experience with the stove if i may.
I did some looking for the replacement and it seems the serial number matters, but i found this,
http://www.stove-parts-unlimited.com/Whitfield-Renaissance-Prodigy-II-Exhaust-Blower-p/pp7602.htm
Common problem for pellet stove's, there's a few similar threads, if the setscrew is in tack I'd start with penetrating oil and a bit of heat, repeat a few times you may get it loose. Same for the fan, a little heat and oil and give it some time to work. I have a butane soldering iron that converts to a small torch, if you've got one or can borrow one that may work better, having the control of the smaller flame letting you focus it on just the hub of the fan and not the shaft or screw may get them to cooperate. If the screw loosens you might also unbolt the motor mounts and get a helper to hold the motor while you tap the shaft, hammer and a small punch being careful not to mushroom the shaft end.
I've used anti-seize on mine for the 4 years I've had it with good results but i remove it a couple times a year. It was pointed out by another member that the repeated heating and cooling of the fan will make them brittle over time and the metal deteriorates, you may be to this point with the age of the whitfield.
Not to derail your question and a PM would be fine but hae you had this stove long? Wondering how long a bag lasts on low and high. Or any other info you may care to share.