New CAT. New aftermarket or used Porsche OEM?

[geraintthomas]

After the issues I've been having with my engine (spluttering when hot after a hard drive, fine when driving normally), I'm pretty sure it's the cat. The sound is coming from the rear N/S, and it sounds like a blown exhaust after a while of driving hard but goes away after a while of driving carefully.

Here's a couple of videos I took of the problem:
https://www.youtube.com/watch?v=i69lltfykW8
https://www.youtube.com/watch?v=tyKCsiF_RJo

I assume I'm correct? I've seen a few things online of cat's failing, and having symptoms of rattling and spluttering when hot. It's exactly what I'm getting and sounds it too. A forum user on here is kind enough to let me borrow one of his cat's he has lying around so that I can see if it is the issue.

If it is, do I buy after market new, or OEM second hand?

The after market new one is here:
React Porsche | Euro Car Parts UK

Or I can get a used OEM Porsche one from Ebay for around the same price.

Buying a brand new OEM Porsche cat is absolutely out of the question as I can't afford it.

Thanks!