The only part you need to replace is the short
rubber line right at the brake itself.
No need to replace the hard line.
Shortleg[Dave]
who has this short line only?
It's best to just have it made...Spiegler or CoreMoto... will run you around 75 bucks..


But also there an OEM line front piece that goes from the rear master cylinder to the steel brake pipe... I bought a new one a few years back, but now it unavailable. If you are replacing lines, you still would need to replace it and figure that one out. Part #7 in the OEM fische...check below..
Possibly, if I had to start all over, I might look at doing just one piece for the whole line.
Photo with new and old front line... with OEM replacement steel line and SS rear.

Rear Assembled

OEM parts page
https://www.partzilla.com/catalog/honda/motorcycle/1999/gl1500c-a-valkyrie/rr-brake-master-cyl