Jeremy, there are several ways to remove rusty nuts, depending on just how rusty they are. First start with hitting the remaining threads with a wire brush, then soaking them in Kroil or PB Blaster penetrating oil overnight. Then tighten the nut ever so slightly to break the rust contact. Then loosen a little, then tighten again ever so slightly then loosen some more and keep this up until the nut is off. Keep soaking the bolt in penetrating oil the whole time. If this doesn't work, then try heating the nut with a torch. This usually expands the nut and breaks it loose from the bolt rusty threads. If this doesn't work, then get out an air wrench and break the sucker off while you are drinking beer with C&W music blaring from the shop radio.