G'day Coolaride, just had a quick look back along one of your build threads, looks like you are moving along nicely with the build.
As far as I know, that grey material is pretty much standard for the wagons, up to & including EK & maybe later, just as a filler on all seat trim colours, as it is not seen when the seat is in the normal position.
I have a HR Prem Wagon rear seat (with fold down armrest that I am hoping to use) & it was still used then, although in a colour to match the rest of the seat.
I would think it is important that it remains a perforated fabric though, to allow the seat to "breath" inhale
& expel air during use as the backs of the wagon seats are covered with load boards unlike the sedan seats which are open to the atmosphere.
