Heat Shield Rusted. Any tips to stop the rattle?

Hi,
On one of my flat heat shields above the exhaust, the hole is rusted out so the OEM nut isn't doing anything. I've tried to get the nut off to add in a flat washer to make it tight, but the thing is so rusted that I cannot budge it even with WD 40. Any tips how to secure it so the rattling will stop? Or how to get the rusted nut off?

Thanks!

 

Slapped some of this shit on that bitch 7 years ago and still solid as a rock

 

Did you attach it right to the frame?

 

Just sand around the big rusty hole on the heat shield (to clean it up a bit) then push a ping pong size chunk of this shit right over and around the stud onto the shield. It won’t go nowhere.....ever!

 

Copy!!! THANKS!