Proportioning valve leaks

I recently had an issue like this with my stainless brake line leaking on my new proportioning valve. Took the entire rear brake line off the car. Turned out the flare got a burr on it somehow and it would just not seal in the new valve. Lightly sanded on it with a file and that solved the issue. It is also not uncommon for flares on OEM lines to develop small cracks. It doesn't cost too much to buy a new line if you need to, but I have also heard that the adjustable proportioning valves can be a problem. I didn't even bother to install the adjustable valve on my car. Just installed the correct proportioning valve.