On the cat joints I'm told that the clearance holes corrode or fret so usual kind of wear on such a joint the studs may need knocking out and bolts fitting, it's the most common exhaust joint fault and in a tight working space behind the wheel but clearly visible, I would expect some kind of insert ring and you should be able to find the PET for the Cayman Gen2 2.9 on the Porsche Cars GB Site.
Hope this is of help.
Hope this is of help.