I'm in a process of replacing head gasket in my 2005 Honda Civic DX SOHC. Today I took off the manifold shield and discovered rust, oil residue and looks like someone welded it or it could be just rust.
I'll try to clean the rust with a wire brush tomorrow. Also my oil is leaking and cylinder #4 only produces 10 PSI. My thoughts are that gasket on manifold worn out and it caused oxidation and rust. Hopefully it won't brake on me tomorrow and I'll reuse it. Or should I get a new intake manifold ?
Looks rusty or welded where it connects to cylinder #4.Here's another pic.

 

First off, that's an exhaust manifold. And, in your case, the catalytic converter is part of the exhaust manifold. Even if you get an aftermarket manifold, you're looking at a fair bit of money due to the exotic materials used in the catalytic converter. Unless you have a leak, I wouldn't purchase a replacement.

 

Yes, you are right. It's an exhaust manifold, I realized it when submitted my post but it didn't let me edit.