Cracked manifold?

[Lance]

I have a 944s 16v when the engine was rebuilt the manifolds were heat wrapped which is great for reducing engine bay temps but it's blowing badly can't tell where it's blowing from but sounds close to the head, tried all bolts all tight because it's wrapped its difficult to feel, are these prone to cracking? Where a bouts is a common place, are the manifolds on a s2 the same as an s1 thanks