I removed the plenum since I'm replacing some gaskets on my 98 GTP. Under the plenum there are 4 water-jet pockets and two are blocked by some kind of material. Its hard to tell if they are supposed to be blocked or not. It looks like some filler material so I poked a hole through it with a screwdriver. I either need to repair those hole seals or open them. It seems kind of weird so what do you think?