Yeah, it could be the lid is a little out of round......test on a flat surface like Formica table & you can usually see where it's lifted.....
Then, carfully hold it at 10 o'clock & 2 o'clock, upside down, against your belly & pull slightly......just a few easy tugs, so as not to really strain the porcelain, just get the metal to flex a little....test again & repeat if you need to.........
We really need a video of this procedure, as it is hard to describe.....
Here's pic of the belly, you know what the lid looks like........
See also about halfway down the page in this thread:
http://weberkettleclub.com/forums/bbq-food-pics/on-the-meatloaf-bandwagon-or-man-my-pants-are-tight/msg92381/#msg92381Some may disagree with this, but I've seen time & again, the older ones contain heat at least somewhat better than newer ones....slight difference in thickness of metal & it can also depend on how much cooking coating is built up on the inside.....