When I changed my headgasket and had the IM and throttle body off the car, I looked at my t/b, and from the backside, there was some black stuff around the edge of the butterfly plate. I cleaned the t/b with intake cleaner, but the black stuff was on there pretty good. It felt almost rubbery, like high temp silicone or something. I'm not exactly sure, but I think it was applied from the factory to help seal the throttle plate when it's in the closed position.