I feel your pain. I had a broken pulley on one my mower's mandrels, and was removing the other one for reference. I ended up shearing three bolts between the two mandrels, and had to replace the "good" one because the two broken bolts were simply NOT coming out (PBBlaster, multiple heat/cool cycles, easy out, etc.). I've never had bolts so stuck on any application before. It's not even the extra $45 for the mandrel that sucks - I had to push mow 2 acres two straight weeks.
If 3/4 are good, I might chance it (NOT something I'd do with the mandrel). You should be able to tell how well it will work by the amount of vibration it has.