Correct now just carefully remove, the bottom of the vent frame is what will bend on you. On these old bolts a couple of tricks:
1. Use the PB Blaster or similar penetrating oil.
2. Try to slightly tighten before you loosen to break the chemical bond.
3. If you have trouble getting the bolt back up in place tie a piece of string to it and you can pull it up through the hole, then tie it off to something when it just starts to enter, once started the string will cut as you tighten but by then you are in. Also don't assemble dry put a couple drops of machine oil on the threads. Good Luck!
