Clogged Cat, Slip Control Warnings, stealership ranting

[HAULN-SS]

I got the code pulled today: P0420 Catalyst Efficiency low-bank 1

Probably cause: catalytic converter defective failure possibly due to

Engine misfire or running condition
large vacuum leak
engine oil leakage into exhaust valve guide seals, piston rings

I guess I am going to have to get this fixed via a dealer, I can't find aftermarket parts anywhere. I thought about trying to pull one out of a junkyard, but not sure if thats a good idea or not. I also can't find anything online that says whether or not the whole manifold has to be replaced, or if the cat comes off. Anyone ever seen one that was the kind of design before? on gmpartsdirect.com I found a listing for "Catalytic converter, malibu, 2.4l " for $126 but I can't quite tell if that's the one for me, or what it comes with, since there are no pictures