I had one that was modified by the previous owner. Sounded good and made some quality turbo whistle - I can't tell you if it's better than other designs but was definite improvement over stock.

I'm not sure who can do a quality job for you for less than an arm and a leg but I'm sure someone here will have a recommendation. See how much it would cost to get done - it might be worth it, but with high labour costs here and most other products being made in China, it'll probably work out more expensive than getting a new one. Good luck mate!