Get some WD 40 or even better by far is PB Blaster. Soak the lug nut holes for as many overnights as possible and during day soak them and wipe off rust that comes out. Use liberally. You can also get a propane torch and heat the nuts before trying to remove the rim heat the rim up.
Otherwise they are going to break and you will have to replace them. It happens. They are not to hard to replace as you can beat them out with a punch and them beat the new ones in with a hammer, use lots of wd 40 or silicone to make it easier and clean out rust first with PB Blaster and some fine emery or wet dry paper and then a cloth with PB on it. Then spray on WD or Silicone and beat them in at least far enough to get a lug nut on them. Then by hand tighten them slowly and they will pull into place.
If you are patient and soak the PB for a couple days, it may work but it is hard to get into lug nuts. Check and see if the lug nuts have a decorative cap which will come off and expose an open ended lug not. Then PB will get in to the threads enough that it should break them free.
Friday, March 2nd, 2012 AT 3:43 AM