I have pretty much same problem on my RX400h, cat was nicked a couple of years ago and had a straight piece of pipe welded in to replace it. Now the pipe has broke away as it joins the centre box. I don't want to fork out £700+ for the complete section and have cat pinched again. I was looking at ebay and RX300 centre box/cat 2 piece kit for £256. Does anyone now if the centre box is the same RX400h to RX300?