Admitting Defeat....Petrol Emissions Woes

[Niall]

Providing the temp sensor is getting above 60 when the car is warm, it will be fine. On these old TUs, its purely used to switch the ECU off of its cold start map where it is very rich.
New plugs would make a difference. If they are wearing out, they can create a weaker spark which does make a difference.
How friendly is your tester? If it only failed on emissions, go out and rag the tits off of it, get it really hot (i know you guys don't know what a motorway is down there but id take it up a motorway in 4th gear to get it really hot) and then drive it in and get it on his machine. If it still fails, see if you can find anyone with a genuine cat you can borrow.
Edit: These fuel additives can make a difference. Ive always found Forte to be good. Expensive but you notice a big difference in the running of the car.