yeah, it's a rust "vein" likely to spread and become a rust 'spiderweb" cause the evil has already begun and that rust will suck in moisture (even in LA!) and grow...not a question of "if" just a question of how fast. Maybe very slowly if you live in the desert and keep it 100% dry and waxed. Up here in damper saltier climes, I would not wait. I'd cut open the vein with a knife or a needle, daub it really well with phosphoric acid (no, not oxalic acid for this) until rust was all gone, let it dry and touch up with hobby enamel or nail polish (lacquer), mixed to match as best you can.