A New and GENUINE Cat fitting kit, a new clamp for the Olive join and some good sealant, a good temperament as it's a f**king b**ch to change at times, my cat bolts had melted and the decat pipes can be a touch longer than the cat so it's bit of a squeeze, to get the lamda out of the cat, unclip it from the car, remove the whole thing from the car, then lock it in a vice, 22MM ring spanner just squeezes over the plug and wallop with a club / big hammer to get it off, you'll be there forever otherwise trying.