Thanks for getting back to us, RickyA.

I've recently spoken to Comp Clutch and this is what they said:

"The problem is due to a cross over in design of the Subaru OEM parts during production of 2004 models. When supplying a clutch for the 6 speed STi, we always ask for a VIN number to ensure proper fittment, unless the customer also purchases a Competition Clutch fywheel to match in which case we ca gaurantee it wil fit all models before and after 2004."

They're going to get back to me with VIN numbers so i can confirm this with Subaru and other clutch manufacturers.