A little bit of JB Weld...
If that's not your problem, it still needs to be fixed before you put any more miles on it (excepting a quick drive to the exhaust shop if you need to farm it out).
Now's your chance to upgrade to headers, and I absolutely would. The manifolds are terrible about warping and cracking. If you manage to get a used one, good luck getting it to fit without leaking. You'll also need a manifold-stretcher (yes, it's a real tool www.amazon.com/Lisle-13000-Manifold-Spreader-Chevrolet/dp/B0009OR94W) just to get the bolts in place.
If that's not your problem, it still needs to be fixed before you put any more miles on it (excepting a quick drive to the exhaust shop if you need to farm it out).
Now's your chance to upgrade to headers, and I absolutely would. The manifolds are terrible about warping and cracking. If you manage to get a used one, good luck getting it to fit without leaking. You'll also need a manifold-stretcher (yes, it's a real tool www.amazon.com/Lisle-13000-Manifold-Spreader-Chevrolet/dp/B0009OR94W) just to get the bolts in place.