How do you know it's brake fluid leaking. I ask, because we see power steering return and or suction hoses weeping and in need of replacement with age very often. This is above the brake hard line to flex line on PS side. So very often brake lines just appears to leak, when actually power steering fluid (ATF)
Typically the flare nut hard line to flex nut, will not just start leaking. Unless some removed or loosened the flare nut. But hard line rusted, it may devolve holes. Or flex line damaged, it will. We find the PS side (all) hard line flare nuts damaged very often, when we do remove them. Seems some issue at factory on PS side of vehicle, with all flare nuts being over tightened, mushrooming the flare nuts.
Flex line damage can accrue with age. But most common damage is due to letting brake caliper hang (dangle) by flex line during as service, where caliper mounting bolts removed.
The way to test/inspect brake line. Is to clean, dry and visually inspect. Have a buddy press brake pedal down hard with IG key turn to on, while inspecting brake lines.
Here's ones very apparently bad (bubble/swell in flex line).