Apparently the BK guy doesn't have much knowledge of the stove either, if he thinks it is a gravity seal. I'm sure they seek out the best help minimum wage can buy, but that only goes so far.
You should feel the rod "cam down" the plate and make the click sound that you are hearing. I've seen that in other BK posts. If you hover over 'forums' above, maybe a search will turn some of these up. That camming action is present both of my stoves but since the hinge portion of the bypass plate isn't held in place on the BK, it's possible the the plate could move a bit in relation to the gasket as it sets down. I would try the dollar bill in several places around the gasket, and also open and close it multiple times to see if my theory about the moving plate holds any water.
That said, it may not make a whole lot of difference. Like black smoke signals said, if you're not having a problem when you run it, it's all good. If smoke is getting past the bypass gasket and is visible outside even after the cat is lit and glowing, I wouldn't like that.
You're on the right track trying to understand how the stove is supposed to work. None of these stoves are perfect, and if you're lucky enough to have a little mechanical aptitude, you can dive in there and fix a lot of problem yourself so that your stove will do the job to your satisfaction. In all likelihood you'll end up knowing more than a lot of the stove store guys out there..