if you have the misfortune to have a dealer NOT stand by a vehicle they sold (un heard of, HUH?)
is this the steel dual pipe that goes from the front along the firewall, down the middle of the van, down the right side of the center of the van to the back?
if so, you can buy O2 Sensor rubber hose, which is high heat proof and PERFECT for this application. it comes in several sizes, so you can find the right size to fit right over the pipes where they are not rusted out.
the pipe and flex hoses total about $400.00 this hose cost about $100.00 for enough to replace most of the pipes, and get rid of the rusting steel pipes.
the only thing that you have to figure out is how to support the hoses so they dont drag and chafe through.
i used heavy zip ties and tied them the frame when i did mine.