On 2002 Pontiac Grand Prix, I've got a brake leak due to corrosion in the tubing run from front to back of the car. I'm looking for a diagram of what is in this tubing tray as I am considering replacing all of it, not just the break line. I need to know the tubing sizes needed and what each is. and things to look out for when reinstalling the lines.

You should still be able to get the correct parts from the dealer on this car, there is also after market parts available at parts stores, corrosion when visible is on the tip of the iceberg. Replacing the entire line is the smart thing to do. Call your dealer and they will tell you availability and the line size. Be critical in not over bending sharp angles, if the line you get is too long and you don't have flaring tools, try looping the extended sections before assembly, be sure they don't interact with moving parts of the car, Hope this helps you and Good luck