The gasket between the air box and the gasket between the intake in the throttle body, are a felt type gasket. Once they get hot, they seal and become almost like plastic in texture. Back during the summer, I was trying to find out why I was getting 10 mpg, and while doing that, I sprayed carb cleaner all over the TB to see if there was a leak of some kind. I didnt find any leaks, but I pulled the TB off anyways. Once I got the tb off, about half gone. I changed that out, and my miles started to go back up....???
I assume that over time, these gasket will deterioate from getting hot and cold all the time.