Exhaust Manifold Catalyst Failure

[dillonmr]

My front cat has spilt on the exhaust manifold front catalyst on my Cooper S R53 JCW. I had it lifted and fount that the cat has completely failed and needs to be replaced (has been temporally welded to kill the noise).

What I want to know is what the feeling on spurious parts verses OEM parts? I don't want to put a performance manifold on her but also don't like the idea of shelling out close to £800 for a OEM part from a dealer (that doesn’t include fitting it).

I've found what seem like good value spurious (pattern) parts but unsure how accurate these are to the OEM part?

Another query I have is that the Spurious part is standard for both the Cooper and S but RealOEM shows different part numbers for the Cooper and S, does anyone know if there is any difference or this a typical BMW trait of giving several part numbers for the same part for different model cars?

Any advise would be great thanks.