Look up from under the dash at where the air vents come inot the cab and you will find the rust if its there. Also it will more than likely have rust holes or bubling on the panel near the lower corners of the windscreen. This panel that runs across on the outside of the car below the windscreen is called the plenum chamber. The chamber part is where the air is drawn into the cab through the grill below the windscreen. It is a big cavity and it is 100% designed by Holden to rust out from the inside out!