These are headers stock right? Anyways I noticed today on the seam for the "header heat sheild there was some black "soot" looking stuff. would a leaky "header" cause drivability issues? And could I just tack weld the hole? The heat sheild is coming off later fro me to see the damage (its too hot now)

No prob. Just soot from something inside the heatshield burning off. Could be anything like a leaf, etc. It doesn't mean the header is leaking.

Mine does that, too.

Yep could be anything burning in there. You should be able to smell the fumes in the bay if cracked. You may be able to see cracks in the header if there'* a leak. You can use a mirror to check hard to see places. I would think, yes, a leaky manifold can create problems if it gets bad enough. I would think it would work on the same principle as back-pressure. If theres a crack theres exhaust flowing without retriction there by decreasing back pressure blah, blah, blah. I may even create turbulance in the flow of exhaust that may have ill affects as well but then I'm not sure if that could create a problem on this car.