Cracked Header - Big problem or let it go???

Being sick of looking at the old rusty heat shield, i bought a can of high temp spray paint and was gonna give it a fresh coat of white, but as i took it off, i noticed there was a decent crack in the exhaust manifold/header, whatever it is...is this something that could get worse, and what could eventually happen? if i have to buy a new one ill most likely go after market rather than a junkyard. are e-bay, no brandname headers ok?
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Yeah, if you can feel exhaust leaking, just get a new one. I recomend a brand name header. Ebay one's are pieces of junk and the welds are notorious for cracking. DC sports makes a really good peice at a good price. I got mine shipped for 270.