I'm not sure if the warranty applies for Australia. I know US Lexus has better service. Most of the recalls they have there don't apply here. Maybe you can try to bring the copy of letter to one of the dealer, even to Lexus Australia. I cleaned my engine with just spraying in ultratune. Helped a bit, but the jitter still there from time to time, but it didn't trigger check engine light. To properly cleaned it you need to open it up, and scrap the grease. It is basically the same as BBQ grill build up. Degreaser chemical spray only does so much.