The top vent is going to be your chokepoint for the WSM when it's well sealed, so it meters the amount of air that can flow through and provide oxygen to the coals. When you have a lot of leaks if your middle section is out of round, the door doesn't fit properly or the lid doesn't fit properly it allows more air to be pulled through your coals which is going to make the smoker hotter.
I haven't had to adjust an out of round middle section, but I've seen several posts on the forums regarding this. It seems to be a pretty common situation, most people say just find out where it needs to be adjusted and give it a bear hug to try and bend it back a bit. As long as you don't go crazy on it and just do little adjustments the porcelain should hold up. You can do the same with your door to give it a better fitment before purchasing a gasket set.