DuoTherm A/C Condenser Fan Blade Removal

I have an older DuoTherm rooftop A/C unit that somehow the plastic condenser fan blade has gotten cocked a little sideways and is off-balance, causing a severe vibration. I took the shroud off, expecting to find a dirt dauber nest on either the squirrel cage wheel or the condenser fan. Instead both were clean -- just the hub of the plastic fan was cocked. From the looks of the rust on the shaft clamp, it's been that way a while and just now the motor bearings may have worn enough to cause the vibration.

My question is this: how do you remove the plasic fan blade ? I tried loosening the clamp that holds the fan hub to the shaft, but could not budge the fan blade off the shaft. I could loosen the screw that that was it. I did not want to try to push too hard for fear of breaking off a blade and really being stuckwith no A/C. Any tips to try to loosen or get the fan blade off the rusty shaft ? I plan to buy a replacement blade and have on have on hand in case I have to destroy the old one getting it off the shaft.