Last I was told, compression fittings are not acceptable on hydraulic brake lines. I have never seen one fail, but i always replace them with proper double flare fittings when i am responsible for the brake repair of a vehicle. It was drilled into my head when i worked for a brake shop that compression fittings are not allowed, true or not.
That said, I've been trying to get my brother to replace the comp. fitting next to his M/C on his Pantera for the last 6yrs. It still works fine.
On my car, before i could do the full pre-bent line, I bought 3 pieces of brake line and 2 unions. I ran one long line front to center, one long line rear to center, and one short line to connect the two. It was ugly, but it was a fix that I knew would pass inspection. My line was rusty on the front from the junction to the frame, and also rusty from the frame to the rear hose bracket, where it developed the hole. This was before i had a line flare kit.
Since owning a flaring kit, I've fixed plenty of lines which were rusty on the back half, but fine on the front half. I cut several inches in front of the rust to where the line is without a doubt fine, and replace the rear section with new... also passes inspection. Line flare kits can be rented or borrowed, but can take some practice to get a decent double flare.
