Nice find
I have used a hammer and large punch to tighten them up......you just have to be gentle. I place the lid upside down on a chunk of wood, and then use a fat drift punch and hammer from the inside. It doesn't take much to tighten the rivet back up. I had to do this on my 26er when I got it. It was so loose that the vent would close just by opening and closing the lid. I had two cooks ruined because of this. The vent spun closed and I didn't notice. I came back to check on the food and the closed vent had choked out the fire. After the 2nd time, I had to find a solution.