Back of engine coolant leak '95 3.0

I noticed a small leak today coming from the back of the engine on my 95 Taurus. It looks like it's coming from a steel hose that runs along the back of the engine. It just looks like it's due to corrosion from the metal bands that were holding it in place. Is this serious - as in "stop driving right away!" serious, or "something I need to have fixed within the next" week serious? I'm guessing it leads to/from the heater? Any advice would be helpful? Also, can this steel line be replaced with something from Gates or the like? An expensive fix?

I would consider it an ASAP fix, because I may just break loose at some point....I beleive I read in an earlier thread about someone replacing the metal hose with regular heater hose.