I'll be interested in your findings as well. My 55.2 6400 already has new lines in the front, but the rear rubber line looks pretty old, cracked, and crusty. I ought to replace it before I even try to fill the brake system with fluid.
Paul,
If it was me I'd replace ALL of the lines (steel and rubber) on your Frank'n truck, they fail from the inside out and you only have one circuit. It's easy to do and doesn't cost that much. No sense taking chances...do it now and forget it for years to come.
Mike B
