I know it was said not to use an impact gun back on page 1 but maybe now it's time to try one. Since the bolt is stuck it's not worth reusing anyway.
Get a good impact with the proper impact socket and give it a try.

 

I don't own an air chisel but I do have a hammer drill. Would that work?

 

If a hammer drill doesn't work I think I might try an impact gun as long as the dealer has the parts.

 

Can you get that hammer drill and bit under the bolt, is the HHR jacked up high enough and securely on jack stands?

 

Hammer drills don't usually allow you to just use the hammer function without rotating the bit. Maybe you mean a Roto-hammer? SDS, or SDS plus?

 

I can't get the hammer drill and bit directly under the bolt because even though the car is on jack stands it's not that high. I thought maybe hammering on the side of the bolt might help. My hammer drill can be set to hammer without rotating.

 

Worth a try! See if it shakes the sleeve and the rust loose.

 

I had someone help me with the rear bolt today. Using a 1/2" breaker bar and cheater pipe it took both of us to get it loose. After many turns it will not come off. While he turned it I looked at the top of the bolt through the engine bay. I could see it turning but that's all it will do. It seems that the welds on the nut have broken loose so the only solution is to cut off the nut. No fun on jack stands as someone has said. What is odd is that it is still quite difficult to turn the bolt. Would that be possible if the welds are broken?

 

That means that the bolt is rusted to the sleeve. Cutting the nut off alone will not allow you to extract it.

 

I just dealt with my driver’s side LCA rear bolt , the nut spins in the cage , I could get a screwdriver wedged in the cage. And that held enough that I could turn the bolt. Mine was apart just last July for the LCA’s to be replaced, whoever did the work didn’t liberally slather neverseize in the bolts threads or shank.
Thankfully I was just going to remove the bolt , lube it and put it back in. Maintenance if you will.
which side of the car are you working on , if you can see the cagenut from the engine bay it must be the passenger side.
if you remove the swaybar bushings , you might have more room to get in there with a Sawzall fitted with a 9 inch blade to cut the cage and the bolt , then a pickle fork to get the bolt out.
if the bolt is seized in the sleeve more cutting is required on the top and bottom of the bolt inside the cavity the LCA fits in.