Regular Cab Black Goop Above Seatbelt?

My drivers seatbelt adjuster (sliding plastic sheets in the cab panel) is all gummed up with black goop. I opened up the passenger side, which is still sliding fine, and there is a square of plastic film with black goop underneath it. It is slumping down and will be getting everywhere, like the drivers side, soon.
so. What is it? Why is it? And how should I clean it up?

 

That should be Butyl adhesive. Absolutely normal, installed at the factory as weatherproofing. Yours has seemed to slip into the trim, try Goo Gone.

 

Copy that. should I try to re-seal it with something when I put her back together? To me it doesn't seem super necessary?

 

It’s not important, it might even be there to prevent vibration between pieces of sheet metal.

 

Amazing, I appreciate it!

 

@oliverbookboots

@BartMaster1234 is correct. It is likely from a "roof silencer pad" (for roof panel vibration prevention) that has broken down and melted from sun on the roof. It is an asphalt based peel and stick sheet added to prevent what engineers call "oil canning" of a metal panel. It is meant to refer to the noise and movement of the old fashioned metal oil cans like the tin man carried in Wizard of Oz. The kind that flexed in and out and they made a kind of popping noise. It was a really common part in our era vehicles. Tundra also has them on the roof. They usually have a shiny foil surface facing the occupant side of the vehicle.