I have noticed that.
The biggest thing that bothers me -- don't ask me why -- has always been, early in the series, when Kramer rails against taking baths and soaking "in your own filth." Yet, later in the series, when the four are discussing bathroom habits (like, do you pee in the shower?), Kramer says "Oh, I only take baths" or something to that effect.
Their joke/story arcs are amazing, but come on! That's just inconsistency. Maybe I'm missing something.