My wife took her GD to have centre and rear sections of exhaust replaced last year, the mechanic was happy to do rear section but said centre was OK and they didn't normally mess with it as getting the CAT bolts out and joint apart normally resulted in the innards of the CAT breaking up = new CAT = £200+
Yup - What a crap design and poor quality of components!
I changed my leaking middle exhaust tonight in preparation for MOT tomorrow.
For info for anyone else doing this in the future - The studs/bolts in the Cat are extremely poor quality so the chances are that by the time the exhaust needs replaced then the studs/bolts & nuts will already be too disintegrated to be of any use. I used a hand grinder to grind the 3 nuts off which then at least allows you to remove the centre & back exhaust boxes from the car. I then set about trying to remove the remainder of the 3 studs from the Cat. Removing these is not the easiest as they are firmly splined and welded on to the Cat. I then ground the heads & welds off the 3 studs on the Cat with my hand grinder again and tried hammering the studs through as hard as I reckon the Cat could stand but no joy. I ended up drilling the studs/bolts out in small stages up to a 9mm hole size to easily handle my replacement M8 bolts and washers I used to rebuild the system. The other complication that I found was that the wiring for the Lambda Sensor is fairly tight so it was a bit of a challenge to get access to drill out the highest stud on the Cat and not damage this wiring.
The jobs definitely not the nicest but it is do-able and if care is taken the Cat can be saved - It would just be so much easier if Honda had used copperised studs or even just nuts and bolts that could be replaced. (I can see why a number of dealers or independents would just replace and charge the customer for a new Cat rather than go to this hassle of removing these studs/bolts the way they are designed)
I would also recommend having access too or buying a high quality set of drills before tackling this unless you have access to some sort of burning equipment to just burn out rough holes in the Cat flange.
