If rust or corrosion is causing a brake line to leak, the first thing to do is double flare the brake line in order to repair the leak. If the line continues to leak after being flared, then the brake line may need to be replaced. Rust and corrosion can cause small leaks to develop which will worsen over time and the line could break completely. The safest route to take is to tow the automobile to a certified mechanic and have them replace the brake line if the double flaring does not eliminate the problem. Do not ever use compression fittings to repair a broken brake line, as this is unsafe and illegal.