I have a Mildura and some experience with it. Not all good, but I think it is a great steam plant and should work for you since my problem may have been "one off". I couldn't hold steam pressure for more than a few minutes, and tried many different fixes with the help of MSM. These involved adjusting the flame and warming the fuel tank to prevent it chilling, but nothing seemed to work, so I sent it back to Australia. I did not attempt disassembly. They said they did nothing to fix or change anything, but in a Skype conference they showed me the Mildura would operate and maintain 20psi WP-- but they fueled the burner from a large fuel tank, not the small refillable tank. The only theory that explained anything was that perhaps a slide valve had not seated on the valve face until it was subjected to transportation handling. Unlikely, but plausible and as I say, the only theory, since I had been doing exactly what they told me to do including my own innovation of making a heat transfer copper block to warm the gas tank. During the time it was back to the factory, I installed an electric motor and smoker in my 72" launch Jax. Then I got busy building other steam launches and I have not gotten back to prove that Mildura will work in Jax.
I do think, based on what I saw in my Skype conference with MSM, that the burner uses gas so fast it chills the little tank. I replaced the refillable tank with a 3" Pendle tank in the hope that will solve that problem. Prior to that I used a copper heat transfer block between the boiler and the gas tank and that stopped the chilling. I also stopped using the 4 cylinder relief valves as they seem to be unnecessary.
MSM provided me a movie showing the Mildura at work with its Stephenson reverser. The MSM steam plant is beautifully made and I can only say that my problem was a mystery and I would not expect on every Mildura. In spite of the long time this problem took, I was glad for the excellent customer service provided by Mr Stuart Rowe at MSM. I look forward to seeing Jax on the pond under steam. Under electric power the launch looks terrific:
https://www.youtube.com/watch?v=pNwwlWkZSE4Here are a couple of photos of the Mildura and my Windemere launch Jax (together with my Grandson Jax. I'd be happy to provide additional detail if you like.
-Carl